The coaches at my dd's gym start by having the kids do rocking bridges, progressing to raising a knee when rocked over shoulders.
Once ready to do the actual kickover, they have feet higher than hands to help them get over.
The Australian section doesn’t get much traffic and is generally used for discussing the system, program changes, specific competitions and things like that rather than skills. You might get more answers if you post in the gymnast section.
My suggestion would be to kickover from a high platform like panel mats, and as you get more comfortable keep lowering them until you've reached the floor. If you don't have panel mats you could use boxes at home or just improvise?