Citroen C3 Passenger airbag light kept.

The warning light turned on because the computer detected a problem and set a diagnostic fault code in memory. "Resetting" the light is done by erasing that code. That doesn't make the problem go away, and you lose that valuable information.

The intermittent problem is still there, the computer caught it again while it was acting up, and it set that fault code again. Have the code read, not erased. It will get you into the circuit or system that needs further diagnosis.