Child visitation rights

I have been divorced for a couple of years and luckily my ex-wife and I are on fairly decent terms (due to the welfare of our daughter) and there have not been any issues with visitation rights YET…

However, I met this guy out the other day and we started chatting. He had just went through a divorce and the courts have given him visitation rights to his children, but since then his wife will not let him see them.

Does anyone have any idea what step he should take next in order for the court issued visitation rights be followed?? I advised him to ask on here himself, but he really doesn’t want to spill his personal issues on here.