Answered You need to bring a motion asking the court to adopt the recommendation of the children's psychologist, and order the non residential parent to counseling. However, if you are referring to the provision in the parenting plan that pertains to dispute resolution, if the plan requires the parties to go to counseling or mediation before bringing an action with the court, you will need to email the other parent and get him to refuse to do what the parenting plan orders. Then, you can bring an action for show cause re contempt of the parenting plan.
Answered The answer to your question depends upon the role the court placed the psychologist in.
Typical roles in a family law matter include only one of the following at a time: custodial evaluator, parenting coordinator, therapist and visitation supervisor.
The broadest of these is the custodial evaluator. Different states have different nomenclatures for these psychologists. California calls them an "EC 730" evaluator. Colorado calls him a "CFI" (custody and family investigator). In New York, he is downplayed for show: "custodial evaluator".
Generally, this role is the most intrusive into the family.
If the psychologist of whom you speak is appointed by the court, then he cannot recommend "mediation". This is a legal strategy most typically offered by your attorney. The psychologist cannot assume the role of your attorney. Consistent with that, the evaluator cannot "recommend" settlement of the matter because as an agent of the court, the psychologist cannot coerce people to settle their family law case.
The typical evaluator always is minimally qualified to perform family law work. They render diagnoses which have no place in a family law setting. So, they "recommend" treatment in the form of "therapy" or counseling which yields copious amounts of money for the therapist who in a later role may refer back another parent to him.
These may be the reasons your ex is balking at all this. He may have figured out there is nothing wrong with him or his parenting. He may have instead read on the internet that the divorce industry features gluttonous psychologists attached to courts. He may have reasoned that he has to challenge the evaluation rendered against him (though perhaps not yet filed with the court) to free himself from the requirement to go to "counseling" - in essence pay to see his child.
This apparatus destroys the custodial parent because litigation will not cease until the child is an adult. As for the child, there is no telling what awaits our society when kids figure out they can trash a parent in court and enjoy the help of court appointed personnel to do so.
I would therefor consider the impact upon your entire family before I would file enforcement motions. Speak with your attorney to ensure he is acting in your best interests and not that of psychologists.