First, you need to know that when you file a joint return, both spouses accept joint and several liability for the entire return. If there are false statements or unpaid taxes, the IRS can hold either spouse responsible, in any amount, and if one spouse has more money than the other or a bigger refund, they can collect the entire debt from that spouse. They don't have to follow your divorce order.
There are two related forms, injured spouse and innocent spouse. Injured spouse applies when you are married, and you don't want your share of a refund to be taken for a spouse's debt from before the marriage.
Innocent spouse only applies after you are divorced. It is a request to not be held responsible for a joint debt that occurred during the marriage. You would need to allege that you didn't know your spouse was cheating on their taxes; that you had no way of knowing that the return was false and that you did not benefit from it. You can also request equitable relief, meaning that even though part of the debt is yours, you have some reason that the IRS should not collect all of it from you.
https://www.irs.gov/businesses/small-businesses-self-employed/innocent-spouse-relief
Both forms are combined in one interview under the "Other tax situations" tab. The interview will first ask questions to determine which situation applies and which form you need.
