Being able to progress in the Echoing Void DLC expansion can definitely be tricky so allow me to help you find all 6 Eyes of Ender.
Before we begin, allow me to give a quick overview of what to expect. Basically, in order to access the new levels within Echoing Void, you need to collect 6 Eyes of Ender then return them to a new level known as The Stronghold. These key items are located in new areas within 6 of the core campaign's levels so let's get to the walkthrough where I'll tell you exactly where they're located.
To find the first Eye of Ender area, enter Creeper Woods and keep going northeast after the bridge at the beginning of the level. You'll reach a big rock cube in the water so head up the rock stairs to the right of it, roll off the top to land on a new path, and keep heading along. You'll fight an Enderman and after you win battle, enter the cave, keep carefully rolling to land on each new platform, and at the end; you'll face an Endersent boss and the Eye of Ender will materialize once the fight is over. After collecting it and opening any nearby chests, feel free to exit via the Return to Camp option in the pause menu as your progress will actually save.
The second Eye of Ender is found in Soggy Swamp. When you reach the Destroy the Brews mission, run to the southeast part of the area and exit via the newly-formed bridge in the bottom-right; making sure to roll over the gap. Enter the cave at the end, be patient with the moving platforms so you don't fall down, and you'll reach some buttons that you push in this order: bottom-left, right, left, bottom, and top. This will allow you to descend to the Endersent boss fight where you can collect your next Eye of Ender.
Next, this third Eye of Ender is found in the autumnal Pumpkin Pastures. Keep following your objective arrow until you reach the area that's pictured in the screenshot below (it has a center patch that's surrounded by a fence) then run southwest from there until you fight enemies in an arena. Once you win, enter the doorway to the left to encounter a bunch of Raid Captain mini-bosses. You don't have to defeat them so run northeast then southeast after the gate closes and a couple of Endermans should show up. Defeat them then activate a button at the very top of this area after entering a stone passageway. This will allow you to exit via a doorway after climbing the southeast stone stairs. Then, fight the Endersent for its respective Eye of Ender. Phew; that was a long one!
For the fourth Eye of Ender, follow along while playing through Cacti Canyon just like we did with Pumpkin Pastures and when you reach the intersection that's depicted in the screenshot below, head southwest through an archway and keep running southwest until you see a cave then enter it. In here, enter another door, be careful of the wall segments that close in on you, fight the arena enemies, and grab the key after the battle. Make sure it stays attached to you and use it in the previous room. Enter the newly-accessible room, fight more enemies in the southwest, grab another key, use it in this area, and enter another door. Snag the yellow key here, haul it all the way back to the first room, use it in the northeast, and battle the Endersent for a much-deserved Eye of Ender. 😅
Thankfully, Desert Temple is fairly straightforward although getting the fifth Eye of Ender here is slightly tricky. As always, follow the mission arrow and as you do so, open the gold key door, run past the Redstone Golem, complete the arena battle, and exit northwest when you reach the junction in the screenshot below. Enter the door after pressing the button, you can run past the Endermans if you want, and keep following along while avoiding the dangerous walls and rolling over any gaps. You'll unlock a door with a blue key and another door by activating switches then finally receive your Eye of Ender after fighting another Endersent. Well, that was tough!
Lastly, we'll obtain the sixth and final Eye of Ender from Highblock Halls. Follow the arrow until you reach the Destroy the Buffet objective which is after a short underground area then exit via a new passageway in the northwest as pictured in the screenshot below. Flip switches to open the gates, enter the door, work your way through, fight an Enderman, take down the last Endersent, and collect the final Eye of Ender. Yay! 😄 Now that we have all 6 Eyes of Ender, go to The Stronghold and return them to unlock The End Wilds.