First, yes he has to file a T1-OVP.
Then withdraw the excess as soon as possible. By default, his financial institution will withhold some taxes on the RRSP withdrawal. He can file a form with CRA asking to be exempt from the tax withholdings, but it can take six month for CRA to approve it, during which he still have to file T1-OVP and pay the related tax, so it’s often better to just withdraw asap with withholdings, and get those back when you file your next year’s T1
On the next year’s T1, you will have to report the T4RSP for the withdrawal. In addition, so that your client doesn’t pay tax on an RRSP withdrawal he didn’t even get to deduct, you will complete form T746, which will provide a deduction for the amount of the excess RRSP that was withdrawn.
Hope this helps.