If your E39 is newer that 09-2001, simply go into the Service Mode and change the AREA from OCEANIA to EUROPE - then all RDS features will be enabled. You may also see an RDS option, turn on as required.

If your car is older than 09-2001, you have an old-gen C23 OCEANIA radio fitted. This is non-programmable and has no RDS. It must be replaced for RDS to work.

Remove it and replace with a BM24 BMW PROFESSIONAL RDS or a BUSINESS RDS radio module from Europe

Easy to find 2nd hand

Or otherwise upgrade to a new-gen radio, fit the BM54 PROFESSIONAL RDS and enjoy RDS & Aux-In capabilities and much more.