How do I change the catalog I see on Lightroom CC?

Hi. I hope someone can help. I've started using my new Windows laptop and decided to start afresh with  Lightroom. (My old catalogs are on my old Windows desktop, which is still accessible.). However, Lightroom CC on my phone is still showing me the old catalog. Please can you tell me how to change it so that I can see my new catalog? I'm sure it's really easy for all you experts out there. 😊 Thank you. 🙏