To get back up, sit with your backside on the ground and your feet/wheels flat on the ground in front of you. Hold say your right wheel with your right hand to stop it rolling away and then, using your left hand on the ground, push yourself up onto your stable right foot/leg and proceed to stand up. At some point in getting up you may want to transfer your left hand to left wheel to steady that but it is not usually necessary. Of course, left handed people or people with stronger left legs may which to hold and support the left wheel with their left hand to begin with.
If someone offers to give you a hand up it is best to hold one of your wheels with one hand while they pull on your other hand, and if they footed one of your wheels so that you don’t roll into them that would help.
Please note: Always wear protective gear. Like snowing, skiing or any form of skating, you will risk falling when riding Chariot Skates. Even after hundreds of hours experience I – the inventor – still occasionally fall. Without protective gear I could have sustained serious injury.