Do you have to do it because they're flat or just because you want to know how to? I know all about flats from my long deceased Aero 50. I t had almost 50K on it when it died and also had tubed tires. I'd guess I did no less than 100 repairs, a ton of tires and who knows how many inner tubes. It sucked having to carry around all the changing equipment in a trunk the size of a lunchbox too
Now don't get me wrong as I have nothing against Vespa, but any two wheeler that has a spare tire on it that isn't just for show, is an experience I'd rather not relive

Hopefully the Symba doesn't have an issue, because I haven't heard of any SYM with one and I have over 5700 on my HD with 40-50% left and no issues.
Jeff