You can amend a return to change from married filing joint to married filing separate, as long as you file the amendment before the original due date of the return.
You can also amend your return to include the Injured Spouse Form 8379, but that form can also be filed on its own without requiring an amended return. Form 8379 lets you (the "injured spouse") get back your portion of a jointly-filed refund if it's seized or offset to pay your spouse's debt.
For more information and instructions from the IRS regarding the Injured Spouse Form 8379, click here.
https://ttlc.intuit.com/replies/3326788
{Edited 2/22/2018: 5:42 PM EST}
