I've been in a similar situation, I didn't have experience riding a gaited horse and was told a few things buy the seller but I wasn't having any luck. I was able to find someone from the area who had experience with gaited horses, she came over and road them and confirmed that they could gait, she gave me some pointers, since then I found no shortage of opinions on what to do.
One suggestion I have is start as a walk, gradually increase the speed, you should feel a sweet spot, I found it pretty noticeable. Now keep him there, basic pressure and release in the bit, some will be easier that others, just depends on the horse. Many other things also and I'll let others with more experience provide there input. Hills vs flat ground, body position (yours) some may be breed specific. I only have experience with Rocky's. Good luck, it's a fun journey