Who does CPAP machine refittings?

So I got diagnosed with sleep apnea, and recieved a prescription for a CPAP machine, right around the same time my step father-in-law retired his CPAP machine for an APAP machine. My wife and I are trying to save some money right now an her step FiL has offered to mail us his old device.

I understand CPAPs need to be customized for each new person, but I have zero clue what type of professional or bisiness entity performs such services or even if it's something insurance might pay for.

Would someone here mind pointing me in the right direction? I live in the Denver metro if that makes any difference or in case anyone has a specific recommendation for me.