Exploration is the main focus of End Remastered, and to reach the End and beat the Ender Dragon, you will have to find 16 custom eyes by exploring vanilla structures and fighting vanilla bosses.
Once you have at least 12 eyes, you can follow them until you reach the Stronghold. You have to put the 12 custom eyes in the portal in order to open it. If there’s a vanilla eye of ender in one of the frames, you can remove it by right clicking on it with a custom eye.
For more information about the Eyes, visit the official CurseForge page.