Possible causes: 1) Overfilling gas tank 2) Releasing starter button early, before engine starts.
To reset CEL: 1) Turn bike off and turn it back on in a minute or two. 2) Turn bike off and let it sit overnight.
You’ll not hurt anything by ‘resetting’ the light. Not sure what your bike recommends. Some bikes will reset by turning on the ‘ignition only’ for 10-15 seconds, or you can try disconnecting the battery leads. When power is restored, the ECU will cycle looking for a fault, and reset itself if it finds none.
What happens when you first start the bike (so it is in neutral, clutch out, side stand down)? If there is an error it should flash to give a code. A number of long flashes for the tens, followed by shorter flashes for the units. This then repeats. e.g. three long flashes followed by five short ones is error code 35.
Rebel500 