I placed the four crystals around the original dragon platform. The dragon spawn sequence began and the original obsidian pillars were replaced with the new/modded pillars and crystals on top. The center was replaced with the building and the new center crystal configuration. I destroyed the outer pillar crystals. Then attempted to destroy the center crystals, which didn't work. I then got on here and your youtube videos to look for a solution. I tried the "/end_island reset" and "/end_island reset true" command. Both state the command is unknown or incomplete command. I also made backups and deleted the DIM1 and DIM_1 folder. The end island was there, but the dragon structures and my man made structures were gone.

What else should I do?

I just got to the end for the first time. I saw end crystals in the middle. the dragon sequence seemed to follow the same as the videos I've seen except the end crystals in the middle are still there, and can not be interested interacted with. They keep healing the dragon also.
I'm playing on 1.21.1 using the modpack
Craftoria version 1.7.2 updated from 1.16.1. First ever load of the end.

I'll try some of the commands tonight, and see if they help

I was able to use the commands. When I did, the current dragon was still active, I tried this until I had 3 dragons. I deleted my end chunks but now the end islands building is sink by about 3 or 4 blocks. (But that's probably because I tried resting the end islands before I loaded the islands)