I have a tanning bed that a three prong plug green ground white neutral and black hot. And I'm needing to make it a four prong plug. So I'm making the adapter so what wires do I put where to make it a four prong(dryer plug)

This sounds like a very bad idea.
What do the instructions say about using an adapter, especially a homemade one?
Can it be used on a 30A circuit, or must it be on a 20A?