Before you proceed further, you should delete your mail credentials on your code. I suggest you move it to the .env file, and change your current one, assuming you unintentionally put your real password.
Deleting lines and pushing the changes doesn't completely delete them, because they are still accessible in older commits.
You should make a copy of all the repo's files (except for .git/ folder), and then force-push it to the remote which will delete the entire commit history like this:
git init
git remote add origin https://github.com/Noname400/mnemonic-colider
git add *
git commit -m "commit message"
git push origin main --force