Then maybe just email him "As you know, your parenting time is every Sunday, but you continually do not show up each week. Please let me know which Sundays you will be available this month and next so I can plan around them. Also, you said you would tutor xx in xx. If you can not commit to a weekly time, I will have to find alternate tutor as xx needs immediate help now as per the CSE meeting on XX."
If he does not respond, second email "I have not heard from you, until I hear from you , I will assume you are not exercising your parenting time. Children need consistency and I do not want to keep telling xx you are coming and then do not show up each week."
Use email or
certified letter so you can prove you tried on your end. As we say on this page for many years...you can not force a parent to parent.....