We have an article with the steps on how you can record daily sales. Let me share it with you.
I understand that it's weekly sales you want to enter in QuickBooks Online, so we'll need to tweak some things, but the steps will remain the same.
We'll have to create a customer account first.
Click the Sales tab, then select Customers.
Select New customer.
You can enter the name Weekly Sales or whichever you like.
The rest of the whole setup process is found in this article: Record your total daily sales. As mentioned above, don't worry that it's saying daily sales. The whole concept is the same and will work for you.
If you have any other questions in mind, don't hesitate to leave a comment below. I'll get back to you as soon as I can.