Tablet problem

I have a problem with my tablet because I can’t see it in my devices and I have the avast free security program from the play store. Please help me my tablet doesn’t have sim and my tablet was stolen.

If your tablet does not have a SIM.
If you does not register it at my.avast.com (or did not install avast! Anti-Theft, only avast! Mobile Security), well… it will be difficult to help…