You may import accrual-based accounts and convert them to cash basis. Click here "Why Accrual import?" 

Adjust in prior year and adjust current year  accounts receivable &/or payable,  via "Income" > "Business" in TTR form

Simply press the button and set "YES". To expose the section to report the GST component. It is important to recognise the GST associated with your accounts receivable & payable values since the GST component should not be part of the reconciling adjustment.

Related Article:

Cash vs Accrual Reporting in Tax Forms

GST Reconciliation - Cash GST reporting and Accrual accounting