A flat scooter tire happens due to one of two conditions: the tire or inner tube has been punctured and leaks or the tire needs to be inflated. Testing for the latter usually helps avoid some extra work if no leak actually exists.
Confirm the suspect tire contains insufficient air by squeezing the tire and checking the tire pressure. Locate your tire pump, remove the tire tube cap, connect the pump, and re-inflate the tire to full pressure. Check the side of the tire for the proper inflation. Allow the tire to sit and check if it deflates again. If the tire retains it's air while sitting then take the scooter for a test drive to confirm it holds the air.
Confirm the tire has a leak by removing the tire and submerging it in a bucket of water. Remove the securing nuts holding the wheel to the scooter rim. Remove the tire with the wheel rim. Inflate the tire until it is entirely full again. Take the full tire and submerse it in a bucket or bin of water. Let the water settle and look for a persistent air bubble stream to identify the air leak location.
Mark the air leak location. Pull the tire out of the water, dry it off, and deflate any remaining air. Unsecure the nuts keeping a split rim together if it applies to your wheel. Use plastic tire levers to remove the tire and inner tube from the wheel rim. Look at the marked location and confirm the puncture or leak that occurs. Throw away the old inner tube if bad. Dispose of the bad tire if the wheel is tubeless.
Use a new inner tube and a new tire if needed. Re-install the tire and tube to the wheel rim. Make sure the inner tube does not get pinched if using a split wheel rim. Secure the nuts for a split wheel rim together or lever both the tube and tire onto the wheel rim if whole. Re-inflate the tire to partial pressure to make sure it seats properly on the wheel rim. Confirm the tire sits right and inflate fully. Reinstall on to the scooter wheel hub. Secure the nuts holding the wheel to the hub and take the scooter for a test ride.
Prepare for an emergency before the trip. Secure a spare tire and wheel rim to the scooter. Pack appropriate tools to perform a tire change in the scooter tool box. Bring a new inner tube if needed in the toolbox as well. Pack a spare shop rag or two in the toolbox for cleanup.
Pull over to the side of the road in a safe location out of the way of traffic. Remove the spare tire from its secure area on the scooter and keep it handy for easy access. Identify which tire has gone flat. Use a tire gauge or tool to let the remaining air out of the scooter. Jack up the scooter or put it on its side on the ground. Use the socket wrench set and remove the securing nuts holding the flat wheel to the wheel hub. Remove the flat wheel.
Secure the spare wheel to the wheel hub. Tighten all the wheel hub nuts. Inflate the spare tire to proper air pressure. Re-attach the flat tire to where the spare tire was held on the scooter. Test the new wheel on a short ride to make sure the wheel works properly. Continue the trip checking the new tire periodically to confirm it works correctly.
