If you do not have hundreds of commits already. You can follow the steps mentioned below.
❕ WARNING: This should be used with care! It also removes the configuration of the repo.
Step 1
Remove all history
$ cd myrepo
$ rm -rf .git
Step 2
Init a new repo
$ git init
$ git add .
$ git commit -m "Removed history, due to sensitive data"
Step 3
Push to remote
$ git remote add origin github.com:yourhandle/yourrepo.git
$ git push -u --force origin master
Source: StackOverflow