There are two options to squash the last N commits into a single commit include both of the below-mentioned options in your answer
If you want to write the new commit message from scratch use the following command
git reset –soft HEAD~N &&git commit
If you want to start editing the new commit message with a concatenation of the existing commit messages then you need to extract those messages and pass them to Git commit for that I will use
git reset –soft HEAD~N &&git commit –edit -m”$(git log –format=%B –reverse .HEAD@{N})”