You'll have to edit the expense transactions you've coded with GST on purchases to reduce the amount shown in line 1B. Or create a journal entry to reduce the amount. However, I recommend consulting your accountant to learn what balancing accounts to use in the journal.
To check your expense transactions, you can run the Transactions by Tax code report. Here's how:
Click on the GST tab.
Click on Run reports and choose Transactions by Tax Code.