Merged the master branch with the develop branch, how to undo the merge?

Question

git

I worked in the develop branch, reached a certain state of the project, created a pull request through the github site and poured the changes into master, created the v0.1.0 tag. After that, I edited the README.md file in the master branch, wanted to get the changes of this file in the develop branch and poured "Merge branch 'master' into develop". After that, the representation of branches, for example, in GitKraken became incomprehensible.
Before:
After:

Some actions were taken after the merger, but they can be torn down if necessary. They are saved separately.
Repository Link: Repository

Answer 1

You need to do:
git checkout master
git reset --hard
git push
-f undo the last commit before the merge

Answer 2

git revert -m1 <merge_commit_hash>