The GST report show box 3 has data,,but I can't link where the data comes form

Hi there, @sg13.

The data in your box 3 can be found on transactions you’ve made. You have to find if one of your transaction has this code: (Please see screenshots below)

You‘ll have to customize a report and add GST code so that you can filter the transaction that I have mentioned above. You’ll have to Run Transaction list by Account then Add column GST code. (Please see screenshot below for your reference)

Also, you can check this article if you wanted to change your Tax rate: Change custom sales tax rates.

Please don’t hesitate to comment below if you need further assistance about this process. I’ll be around to help you out. Take care.