“Can It Be Love” (1992)
“Tim and David want to have fun during vacation so they join a private detective agency. Their first job is to find a delta girl who has inherited a fortune.“
The movie is set in Fort Lauderdale, and the heiress the two private detective guys are after has a birthmark.
You can watch the complete movie here:
I am pretty sure this is your movie. If you agree, then please select my answer as Best Answer, there is an option for that.