how to undo bundle update

There is one obvious way:

git checkout -- Gemfile.lock

and then run

bundle install

It assumes you use git - but who does not now days, I have everything in git.

ruby-on-rails rvm bundler

I went into Github, copied my old Gemfile.lock that I wanted and pasted it into my Gemfile.lock in my code and then ran bundle install.

CodeHunter