Where is the reset switch for rear air shocks of a 1999 Lincoln Town car?

The 1999 Lincoln Town Car doesn't have a reset switch for its rear air shocks (or air springs, as they're more accurately called). There's no such switch on the car itself. If the air suspension is malfunctioning, the problem needs to be diagnosed and repaired, likely involving checking the air compressor, lines, and the air springs themselves. A mechanic specializing in air suspension systems is the best resource for this type of repair.