For those using RBENV for managing ruby versions, whenever you install a different ruby version and then you'll be faced with the following error(not 100% same lol):
rbenv: bundle: command not found The `bundle' command exists in these Ruby versions: 2.3.3 2.4.4 2.5.7 2.6.5 2.7.0
Both these commands will be helpful in fixing the issue.
gem update --system
bundle update --bundler