TurboTax online accounts cannot be combined or merged.
If you are going to be filing as Married Filing Separately then you will need to create two new online accounts, one for you and one for your spouse.
You will not be able to use the online account that you used for Married Filing Jointly.
This assumes that you have not filed your 2023 tax return.
If you have filed the 2023 tax return as Married Filing Jointly you cannot change your filing status to Married Filing Separately after the due date of the 2023 tax return, April 15, 2024.
Are you saying that you now want to combine the two separate accounts back into one account so that you can file jointly? There's no way to do that. Pick one of the separate accounts to be the primary taxpayer (listed first) for the joint return and change the filing status to joint. Then you have to manually add the other person's information to the new joint return.