You indicated that you are using TurboTax Online. With TurboTax Online you have to use a separate user ID for each return. You cannot prepare another tax return with the same user ID that you used for your own return.
See the FAQ at the following link for instructions to start another tax return with a new user ID.
https://ttlc.intuit.com/questions/1894512-how-do-i-start-another-return-in-turbotax-online
You cannot use TurboTax to do tax returns for other people if they are paying you to do it.
