There isn't ANY way to re-set anything on that SRS system.
The only reason for a light is if there is a FAULT. The cars between 1984-87 have no memory OR ability to recall faults. The dealer should have a test-adaptor that can find the problem though.
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)