(Make sure you don’t accidentally sign up for a subscription service… you have to hunt for the “free” buttons with each agency.)
You can add notes/explanations to the report for anything in dispute.
Before you worry about fixing the credit report – see what’s actually on it. I thought (but very well could be wrong) that late payments went away after 5 years – so your soon-to-be-ex’s late payment issue might not show.
