Yes, you can file form 8379 after you have filed your return.
Answer the questions carefully so that the IRS can refund the share of the refund which belongs to the injured spouse.
To fill form 8379 in TurboTax, go through the amendment process, fill in form 8379, then print out that form and send it to the IRS. Don't send form 1040X as nothing has changed in your tax return.
To file Form 8379 - Injured Spouse, please read this TurboTax Help topic.