How do you make delta9-THC?

Answer 1

You can't 'make' Delta-9-THC.

THC (for space purposes) is a chemical found in (amongst other plants) Cannabis.

You can 'extract' THC from the Cannabis plant and concentrate it, but you can't 'make' it.

Of course, if you are a major pharmaceutical company, or own an advanced scientific laboratory, you can use other chemicals and processing to produce something like THC, but it isn't natural THC.

Delta-9-THC aka Tetrahydrocannabinol.