Performing the Eternal Ritual to Return to the Overworld
To return to the Overworld from the End, you can perform the Eternal Ritual. This method is not simple, but it allows for a return.
Locating the Eternal Portal
While exploring the End, you may discover ancient ruins. These ruins contain a structure known as an Eternal Portal. An Eternal Portal consists of a frame made of 
Runed Flavolite and six pedestals arranged around it. These structures are the remnants of grand portals that once connected the End and the Overworld.
Eternal Portals generate in regions of the world. The world generator attempts to place one Eternal Portal within every 40x40 chunk region. Each portal will be at least 12 chunks away from any other portal.
Activating the Portal
To activate an Eternal Portal, you must complete two steps:
1. Recover the Frame: The Runed Flavolite frame may be destroyed. If it is, you must repair it. 2. Place Eternal Crystals: Six Eternal Crystals must be placed onto the pedestals surrounding the frame.
The portal will become active immediately after the final 
Eternal Crystal is placed.
Obtaining Materials
Both Runed Flavolite and Eternal Crystals, which are necessary for the Eternal Ritual, are acquired through an Infusion Ritual.
Covers the mod's in-game guide topics: Eternal Ritual Eternal Portal