To reposition an enemy by flipping them, you just need your DM's buy-in that it's possible or reasonable (because ruling on that sort of thing is the DM's job), and then they and you will use the Improvising an Action rule to resolve it. It's a simple process:
Describe what you're attempting
The DM decides if it's possible
If so, they tell you what to roll
When you describe an action not detailed elsewhere in the rules, the DM tells you whether that action is possible and what kind of roll you need to make, if any, to determine success or failure.