You cannot simply remove a worldgen pack from your world. The way to do so involves completely resetting your dimension, so we do not recommend it unless you have a good reason. In order to do so, you must follow these three steps:
1. Ensure your world/server is stopped, and remove the worldgen datapack.
2. You must completely reset the dimension that the worldgen pack was affecting. For the nether and end, this is done by deleting the world/DIM-1 and world/DIM1 folders in Vanilla/Fabric/Forge, and world_nether and world_the_end folders in Spigot/Paper, respectively. It's more tricky for the overworld - either just reset everything, or ask for further help.
3. You must remove all biome entries from your level.dat. If you do not know how to do this, ask for assistance. There will be tools for this later.
