No the child wants to move with me and doesn't like his life at fathers. Father consistently yells at him
Have you ever heard the phrase, "The grass is always greener on the other side of the fence"?
Your child is a tween. Even if Dad were Dad of the year material, it is likely that your child would rebel.
(Frankly, if you asked my teen, my teen would say that I yell at her constantly.)
when questioned the DM could not recall how he attempted to contact her a week after his decision
You HAVE to stop dwelling on this. Regardless of what the DM did, it was 4 YEARS AGO. Any change you wish to pursue has to be based on the current circumstances.
If you are serious about wanting to be more involved in your son's life, move back to CO; the current order is out of CO, and CO retains its jurisdiction. Anything you'd want to file, you would have to file in CO, and that's easier to do if you are living in CO.
Exercise your parenting time to the fullest, realizing that most courts would realistically not ding a parent for following local, state, and/or CDC guidelines during a pandemic. Become involved in the parenting groups related to your son's activities, both in and out of school.
Age/time passed can be a change of circumstance, but you have done nothing to improve how you would look in court. You CANNOT go in and say "I want a change in custody because the DM got it wrong 4 years ago." That's water under the bridge and will not fly. You CANNOT allege abuse without RECENT proof, because you've left the kid there for 4 years. It's not like you've got a founded case with CPS and Dad's on the child abuse registry. (And no sane parent wants that.)
I hope you have been in therapy. In fact, therapy would be good for the whole family.