I need to change the filing status. It says single and should be married filing separately. How do I change that now

Did you e-file already?   If you have not e-filed, you can go to MY INFO and click your name, then go back through the screens to answer the questions so that you can file married filing separately.   You must say that you were married in 2024, and then you will be asked if you want to file together with your spouse--say NO to that.   You will have to enter some information about your spouse a little later.

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