How to add available shared runners to GitLab project?

Only one gitlab runner is available in my project. However, in the runner page I have multiple other runners listed. How do I add these runners to the project such that a runner will be randomly selected to execute the build? The runners are running in Docker containers and I am using a self-managed version of GitLab.

These are the runners I have available:

Only runner1 is currently shown in /settings/cicd under Runners: