Dear Bro, don't get confused with the confused statement stated above [Fuel Retarder :S]:)....! If possible, take a snap shot of the connector area and upload here. As per my opinion, if it is TIMING retarder, it should be marketed as timing retarder, not spark timing ADVANCE Processor (STAP).
Usually the STAP is configured as follows:
1. Switch to CNG mode, advance the timing from distributor. Then try to optimize the gas level by adjusting from 17" bolt of "T".
2. Once the gas mixture has been set, switch to petrol mode and adjust the timing from distributor according to petrol.
3. Convert back to CNG, keep the CNG/LPG micro switch to "CNG"(your model specific) and turn the 3 and 1 micro switch to "ON", while 2 and 4 to "OFF". This will set an angle of 3 + 12 = 15 degree.
(micro-switch-1: 3 degree, micro-switch-2: 6 degree, micro-switch-3: 12 degree, micro-switch-4: 24 degree)
4. Setting done.