Ok so I was tinkering with the stuff cuz i had the same problem if you want to get a World into a version of minecraft lets say from 20w13a to 20w14infinite.
1) you have to have atleast 2 worlds for this 1 the world you want to change versions(from now i will be reffering to this as w1) and another that is in the version(from now i will be reffering to this as w2)
2) after you have the worlds close minecraft and go to a folder ".minecraft" and into "saves" there you should have the 2 worlds
3) go into the w2 copy a file named session.lock
4) paste that file into w1
5) start the world in selected version and BOOM you got the world there
Hope it helped