How to remove commits from a pull request

I did a pull request but after that I made some commits to the project locally which ended polluting my pull request, I tried to remove it but without any luck.

I found some similar questions on StackOverflow but I can't apply what's in there. It's my first pull request on GitHub so it's kinda strange to me how all of this works.

The highlighted commit is the one I need to keep and remove all the other stuff. It becomes the fourth commit in the history because I make some merge stuff.

my git log

Can someone please explain what's going on and how to fix this problem?

Solution

You have several techniques to do it.

I recommend of reading this answer:

How can I move HEAD back to a previous location? (Detached head) & Undo commits
It will explain in details what we want to do and how to do it (revert).

TL;DR; (from the recommended answer)

Here is the most simple solution to your problem:

# Checkout the desired branch
git checkout <branch>

# Undo the desired commit
git revert <commit>

# Update the remote with the undo of the code
# The force is a tricky flag since it will force the push but
# your administrator can block it, so if it's not an option you
# can delete the old branch and push it again
git push origin <branch> --force

The revert command will create a new commit with the undo of the original commit.