If you have an access to your Plesk server over SSH, you can manage Ruby
versions via the command line. The commands must be run from the
application root directory, that
is /var/www/vhosts/<domain_name>/<application_name>, where
<domain_name> is the web site’s domain name and
<application_name> is the name of the Ruby application.
Plesk tries to keep in sync the selected Ruby version for the
application. Run the following command to check the current Ruby
version:
ruby -v
You can also use the rbenv command line utility for Ruby versions
management. For details, refer to
https://github.com/rbenv/rbenv#command-reference).