Haven't tried a scooter but they should be the same as motorcycles...
Glued on.
Some use air pressure between the grip and the throttle sleeve.
My DH uses a long thin flat-bladed screwdriver to pry the grip up from the throttle sleeve at the right end of the grip.
And a spray of WD-40 up underneath the grip. It takes a lot of screwdriver movement but once the glue has been released,
a few twists of the grip while pushing from the left end of the grip and the grip slowly comes off.
If you pull on the right end of the grip, it acts as a "Chineese" handcuff and holds tighter to the throttle sleeve.
A bit of soapy water cleans up the WD-40 and aftedr drying, the grip is ready to slide back on.
No glue is needed in most cases, just use saliva as a lubricant or if you want some glue=action, use hair spray.
Real grip glue is usually needed for dirt riding where there are tremendous forces applied to the handlebars through the grips.
scoot safely,
