use
The proto use (or proto u) command will download and install all tools and plugins from all
parent .prototools configuration files, and any versions detected in
the current working directory (if not defined in .prototools).
If auto-clean is enabled, the command will also remove any stale or unused
tools.
$ proto use
This command does not install tools for versions pinned in the global
~/.proto/.prototoolsfile.