I am not a mechanic (not even close), but would this work?
In a home garage or safe place, siphon all of the gas from the tank into a container with measurement marks (.25 / .5 / .75 / 1.0 litre or gallon).
Now, pour .25 litre of gas back into your tank. Cap it. Start the scooter.
Note whether the fuel light comes on and fuel one bar indicator flashes. If so, then .25 litre is below the threshold to trigger the alert.
Now, pour another .25 of gas back into your tank. Cap it and start the scooter.
Note whether the alert goes away.
If you can add smaller amounts and then start her up, the more precise your measurement would be.
In the end, you will have added enough gas to turn the alert off.
Perhaps, with the knowledge of how much you have added and an accurate km per hour gallon, you can do the math and calculate an approximate number of miles left when the alert surfaces.
In the eyes of more experience riders and mechanics, this recommendation might fail on several fronts. But, I only offer it in the spirit of providing a solution, good or bad. YMMV.