I filed single but it needs to be changed to married filing separate. My return was rejected but i can't make the change
You enter/change your filing status in MY INFO.
When you enter your own information in My Info, you have to answer the question "Were you married?" If you click the button for Married, then a drop down will appear that asks, "Do you want to file this return together with your spouse?” Your answer needs to be NO. Then it will ask for information about your spouse—-their name and SSN which you must enter. EACH spouse has to file their own separate return. And you have to follow all of the rules which include that if one of you enters itemized deductions, the other one must also itemize. Or…you both use standard deduction. If you are in a community property state there are additional rules and more information to enter.
If I am filing a separate return why do I have to list my spouse’s information on my return?
Even if you file separate returns (the worst way to file) you each have to list each other's SSN's and some other information on your own tax return. The IRS can then cross check to make sure you are not "double dipping" for itemized deductions, dependents, etc.
If you are in a community property state, there is more information that will be needed.
Community property states: AZ, CA, ID, LA, NV, NM, TX, WA, WI
https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states
https://turbotax.intuit.com/tax-tips/marriage/five-tax-tips-for-community-property-states/L4jG7cq7Z