How to switch from married filing jointly to married filing separately

If you have not e-filed, you can change it.  But----- You might be simply misunderstanding how it all works-----filing married filing separately is usually the worst way to file.   When you file a joint return, the refund or tax due is calculated based on the total amount of income----when you added your spouse's W-2 you just saw the result of all of the combined income.  It would have been the same result if you entered her income first and then added your own.  It is not "her" refund that is being lost.    

WHY DID MY REFUND GO DOWN WHEN I ADDED ANOTHER W-2?

You started off with your first W-2 and your refund looked high?  Then you added another W-2 and it stopped looking so good? That is normal.  When you added more income, your tax liability increased, so you saw your refund decrease.  The program began by giving you your standard deduction—- which lowered your taxable income.  (if you are filing joint it took $27,700 off your income right off the bat)   So you are not being taxed on as much of the income on that first W-2.  Then you added taxable income--so the refund went down. Your refund (or tax due) is based on the total of your income, not “per W-2.”  

And…adding income may affect other credits you were getting like the earned income credit.

Wait until you have entered ALL of your income and credit/deduction information.  You can't really tell anything until it is all entered.  That “refund monitor” does not mean anything until everything has been entered.

https://ttlc.intuit.com/questions/2273878-why-did-my-refund-drop-when-i-entered-another-w-2

If you want to file separate returns --- that will be TWO tax returns using TWO accounts and two user ID's -- one for each of you.    When it asks you in My Info if you were married in 2023, you will need to say YES.  Next question asks if you want to file together with your spouse. Say NO.   Then you still have to enter some information about your spouse---name, date of birth, SSN.   And you will have to choose whether you will use standard deduction or itemized deductions because you both have to file the same way.

Your spouse will have to do the same thing on her return and enter YOUR name, date of birth, SSN, etc.  

Then .....you both have to follow all the strict rules of filing married filing separately.   If you are in a community property state it gets more complicated.

If you were legally married at the end of 2023 your filing choices are married filing jointly or married filing separately.

Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $27,700 (+$1500 for each spouse 65 or older)  You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit. 

If you choose to file married filing separately, both spouses have to file the same way—either you both itemize or you both use standard deduction. Your tax rate will be higher than on a joint return.

 Some of the special rules for filing separately include: you cannot get earned income credit, education credits, adoption credits, or deductions for student loan interest. A higher percent of your Social Security benefits may be taxable. Your limit for SALT (state and local taxes and sales tax) will be only $5000 per spouse. In many cases you will not be able to take the child and dependent care credit. The amount you can contribute to a retirement account will be affected. If you live in a community property state, you will be required to provide additional information regarding your spouse’s income. ( Community property states:  AZ, CA, ID, LA, NV, NM, TX, WA, WI)

 If  you are using online TurboTax to prepare your returns, you will need to prepare two separate returns and pay twice since with online, you get one return per fee.

https://ttlc.intuit.com/questions/1894449-married-filing-jointly-vs-married-filing-separately

https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states

https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separately