If your efiled return was accepted, you will have to wait to make the change. Once you submit your return to TurboTax for efiling, it is just like dropping your return in the mailbox--you can't get it back. If the IRS rejects your return, you can make the changes, fix the reason for the rejection and resubmit it. If the IRS accepts your return, you should wait until you receive a refund (if you are getting one) and then you can prepare, print, sign, and mail an amended (changed) return form 1040X to make the changes. Form 1040X is estimated to be available in TurboTax on 2/22/19 but the date has changed at least 3 times. Do not change your original return until you begin the amended return.
Did the return include only your income? If so, and you don't want to file jointly with your spouse, then you can just change to Married Filing Separately on your amended return. Your taxes may be higher since many credits available on a single return are not allowed on a MFS return.
Your other alternative is to file Married Filing Jointly and include your spouses information. It is almost always better to file MFJ than MFS. It would be a little more complicated to change to MFJ especially if your spouse already filed MFS.
