I’m not a GIt expert. This is just how I do it.

git fetch origin
git reset --soft master
git commit -m "commit message"
git push -f origin nameOfYourBranch

1st line fetches the latest code from the main repo.

2nd line resets your local branch the latest stage of the master branch

3rd line is just a regular commit

4th line is the force push.

This will put all your changes into 1 commit and add it to the end of the master branch.