Once you receive your quarantine release (different email than your test results), you can take down your Q flag.

On Tortola, you can go to Road Town Police Station, West End, Cane Garden Bay (but call first to make sure it's staffed), or East End.

Anegada (Govt. Building) and JVD (Great Harbor) each have a police station.

Someone can offer VG guidance. I know there is one in Spanish Town but not sure about others.