I accidently created a world in a single biomes however i have been building on it for a while and dont want to get rid of my progress but i would like other biomes is there anyway i can changed the world generations settings in the files of the world or wherever so that newly loaded chunks will load in with different biomes other than plains https://100001.onl/
Probably the easiest way to is create a new world and copy its level.dat file over, replacing the one in your world; make sure that you empty your inventory (including your ender chest) into chests as it will reset your inventory, as well as reset your location to wherever you were in the new world (you can avoid this by recording your coordinates and going to them in the new world). You can also save your inventory/position/XP level by using NBTExplorer to copy the "Player" tag from your world to the new world's level.dat file (replacing its Player tag). If you are on a version prior to 1.16 you can also edit level.dat to change "generatorName" to "default" (since 1.16 a complicated "WorldGenSettings" tag is used and I'd advise not trying to edit it).
You'll also want to use the same seed (in the saves menu select your world and click "recreate" and change the world type) because the shape of terrain, as well as the location of slime chunks, are based on the seed and this will minimize chunk walls between old and new terrain (I don't think the terrain blending feature introduced in 1.18 works in this situation, only when upgrading from an older version).
Also, you can prune the world by deleting regions which do not contain anything you've built so you don't need to travel as far to find new terrain; divide the block coordinates by 512 and round down, e.g. r.0.0.mca is from 0, 0 to 511, 511 and r.-1.-1.mca is from -512, -512 to -1, -1 (there is a calculator but the site is currently down).
As always, before doing anything, especially pruning the world, make a backup of the world (you really should be making backups of any data that is important to you, I've seen far too many people lose their worlds for any number of reasons).