Primes

I lost my key and all i have left is the flat.What shoudl i do.?The car is a 90 lexus Ls

Hi, my brother just gave me his 1990 ls and the car works perfectly except for one problem. The remote control feature built into the key nom longer seems to work. I've tried replacing the battery and flipping the remote key switch on and off but still no luck. Has anyone else had a similar problem? Any suggestions on how to fix it?