Here are the steps to add the runner working in project A to project B.
You require the following:
- Be Master of Project A,
- Be Master of Project B.
- Step 1. Add Runner to A.
- Step 2. Go to Settings>CI/CD>Runner Settings of Project A.
- Step 3. Edit the desired runner properties. Uncheck the "Lock to current projects" box.
After the previous steps, the same runner will be available in Project B.