With any 2-stroke (chainsaw, weedwacker, outboard, etc.) that exhibits low compression, the first thing is to look into the cylinder. If the piston and the bore are scored, it's not simple. If the piston skirt looks good through the exhaust port, it's almost certainly rings. They could be stuck or they could have been run hot and lost their temper so they don't have enough tension, or both ...
First step is to get a compression gauge/meter. Do a dry test. Say you get 20 PSI (really low) and then you squirt some motor oil in through the plug hole (any kind is OK for a test) and test compression again. Say it's 80 PSI the second time. OK, we have found an issue - ring seal.
Lay the motor down with the plug holes facing straight up. Plugs out position the pistons so they are above the ports. Get some rifle bore cleaner for carbon fouling (I like Break-Free) and put a good slug in each cylinder overnight. Come out the next day, hang the motor on the fence or tailgate and spin it over with the plugs out until it stops spitting liquid. Pour a bit of pre-mix in each cylinder, put plugs back in, and yank that starter rope. It should sputter to life for a few seconds.
Now pull it agian and see what it feels like? If you can feel compression , you are half way home. If it's still weak, the rings are shot ... After a soak and short run, it should meter out higher on the compression test. 60 PSI and above, you have a runner. Below that, you have an overhaul to do.
Little motors are not hard to overhaul. Take your time and make sure all the gaskets seal well and you'll be fine