What are the steps before CRA freezes bank accounts and what does it take to resolve?

My tenant has continually been late on rent payments and while I’ve tried to work with him for several months, he admitted last month that the CRA has recently frozen his bank account (and therefore struggled to pay rent last month - was eventually paid by his girlfriend). I am proceeding with eviction however was curious what it takes for CRA to freeze an account, and also what it takes to unfreeze an account. He keeps saying he’s working with them and they will unfreeze his account “tomorrow/next week/next business day” but so far it has not happened, so was wondering what steps he would have to take to resolve.