If you are not familiar with it you can search for motorcycle tire zip tie method or leave that off. It works great! I used this method to replace my motorcycle tires a few years back but I am not sure if it will work with a smaller diameter scooter tire.
Basically you buy a few dollars worth of big zip ties and put them around the new tire that is going on the rim. You tighten them tight! It brings the two beads together and you can then use your body weight to get the tire on the wheel. Then you cut the ties and pull them out. Here is a pic of my rear wheel right after I popped it on the wheel.
The best thing about it, well besides not paying someone for the work, is that you do not scratch your wheels doing it because no tire irons are employed but I don't know if it will work on a smaller diameter tire! What have you got?