Amend the separate return that was already filed and change the filing status to married and filing together, then add the spouse and the spouses information.
See this TurboTax FAQ for help with amending:
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
