Welcome to the Community! It's great that you're using QuickBooks Self-Employed to simplify the management of our business. I can explain your options for sales taxes.
When categorizing your transactions, you can select different provincial tax codes for customers in different provinces. Here are the steps to do this:
Select Transactions towards the bottom of the app.
Click the transaction you want to apply sales tax to.
Toggle Include sales tax to on.
Below this, click on the provincial sales tax section, then select the appropriate province.
You'll then have a provincial tax code other than your own province's applied to the transaction. You can learn more about categorizing and applying sales taxes to your transactions in the following Community articles: