How can I update my Magic Jack phone device in my Mac OS X 10.15.7 running MACOS Catalina:

MagicJacks don't use drivers, so there is no updating them. they have always been "plug and play". is yours the first generation MagicJack that does not have the ethernet port? if it is, you should upgrade it to the MagicJack Go that has the ethernet port. IMHO, the first gen unit was extremely unreliable in the first place.

Try contacting the Magic Jack developer to see if they provide an updated version that runs on macOS Catalina.

Ref: How to contact an app developer - Apple Support