This may sound silly, but did you try to re-inflate the tire with a bike pump (you’ll need a valve extender)?
If you did and it’s not holding air, then:
- Do you know how the tire went flat? If you got a puncture in it (nail, thorn or something else), you’ll probably have pretty good luck using tire slime which is easy (happy to send more info on how to do this is this is the case).
- If it went flat with no obvious cause, then a pinch flat is more likely (tube inside tire got pinched on the rim and is probably torn open). For pinch flat you’ll need to remove the tire and replace the tube (this is more challenging, but procedure for changing tire on most scooters is very similar).