Yes, you would need two separate accounts to file as Married Filing Separately using the TurboTax online editions - https://turbotax.intuit.com/personal-taxes/online/
To change your current tax return from MFJ to MFS and you have already entered all of your spouse's tax data, it would be simpler to just clear the return and start over.
If you have not paid for the online edition you are using, have not filed your tax return or registered the Free edition, then you can clear your return and start over. Click on Tax Tools on the left side of the program screen while working on the 2019 online tax return. Click on Clear & Start Over.
