You don't need to do it in a separate return. In order to make a return together follow the steps below
To prepare your returns together using TurboTax Online:
Sign in to your TurboTax account
SelectStart a new return
Select the TurboTax Online product you wish to use, and indicate how you did your taxes last year
On theWelcomestep, selectMy spouse/partner and meunder the questionWho are you preparing this return for?
Follow the prompts to enter your personal information. On theWhat's your marital status?step, selectMarriedorLiving Common-law
Do you want to prepare your returns together?, selectYes
SelectContinueand proceed with completing your returns
If you’ve already started your return but haven’t indicated that you want to prepare together, you'll need to start a new return and indicate that you want to prepare your spouse or common-law partner’s return together with yours.