To file a separate return for a dependent in the Online version you need to set up a new account separate from yours. Online is only good for one return per account. You can use the same email address for 5 accounts. You can probably use the Free Edition
Https://ttlc.intuit.com/questions/1894512-how-do-i-start-another-return-in-turbotax-online
Be sure on the dependent return you check the box that says you can be claimed on someone else’s return. If their only income is W2 and under 12,550 they do not have to file a return except to get back any withholding taken out.
Filing requirements for a dependent
Simple ... open a new account for them using a different userID and password from your account ... do NOT try to use your online account again for their return. AND since they are your dependent they MUST indicate they will be claimed as a dependent on their return.
If they qualify you can use one of the 8 IRS FREE FILE options ... for 2021 your AGI has to be $73K or less ...
https://www.irs.gov/filing/free-file-do-your-federal-taxes-for-free
Or use the TT free option : https://turbotax.intuit.com/personal-taxes/online/
If their only income is W2 and under 12,550 they do not have to file a return except to get back any withholding taken out.
This is correct for Federal, but State may be different.