You are going to have to take it apart, the basic "job" is to replace the drive belt, the perfect time to replace the rollers with Dr Pulley slides and weights. How many miles on the scoot? While it's apart use emory cloth and clean the clutch surfaces and drum surfaces, check for clutch shoes that don't retract and look for trash getting in the way, check for broken springs
not pulling the shoe back, look for uneven wear on the shoes, heavily glazed areas on the shoes, clean everything, blow with compressed air to remove all the dust.
There are good write-ups in this forum telling you what tools are needed for the job, where to buy the drive belt (Carpimoto, the $50 to $60 belts are junk and WILL NOT last more than 1500 miles). Download a maintenance manual, it's not a hard job, take your time, pay attention to detail and you should find what's causing the clutch to stick.