Is there a way to get the missing End Exit Gateway Portal back?
Solution 1:
It seems like you're asking about how to fix or replace your End gateway portal.
The first couple times when you revive the Ender dragon and kill it, a new End gateway portal will appear at the edge of the main End island.
On Java Edition, I believe 16 End gateways are the limit that can appear in a given world, and on other versions of MineCraft it's even less.