Yes, you can amend the tax return to change the filing status from single to married filing jointly.
You can prepare an amended return and send it along with the ITIN application.
If you are applying for ITIN for your spouse, she should be on the tax return.
The IRS will need the original documents relating to ITIN to be attached for verification or get the documents certified by a Certified Acceptance Agent or get an appointment from the nearest IRS office and get the documents verified.
@breaker581 [Edited 03/28/22|11.28 am PST]
