How to transfer changes from one directory to another, similar to git merge?

Question

git

The point is this. Each api version in a separate directory and new api versions are created by copying the previous api version, 3 api versions are supported, the fourth is deleted. Versions appear every 1-2 weeks. This is a working moment; other options do not suit us.
Example:
3 versions exist
21
22
23
We found a bug in version 21, which is critical and needs to be fixed. If he is 21, then the rest are the same.
Problem:
Since we are copying the code, we need to transfer changes from version 21 to versions 22 and 23, a lot of manual work and there is a chance that something will not be transferred and there will be new bugs.
Question:
Are there any tools that will allow you to transfer changes across files, in fact the same as git merge is only needed for individual directories?

Answer 1

make a commit with a fix in one branch, transfer to the rest via cherry pick - if the versions are in the same repository. or try through patches - if in different ones.