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$gem install bundler -v 1.16.4 

Successfully installed bundler-1.16.4
Parsing documentation for bundler-1.16.4
Done installing documentation for bundler after 3 seconds
1 gem installed

$bundle -v                    

Bundler version 2.2.17

$gem uninstall bundler

Select gem to uninstall:
 1. bundler-1.16.4
 2. bundler-2.2.17
 3. All versions
> 2
Successfully uninstalled bundler-2.2.17

$bundle -v            
Bundler version 1.16.4