Thanks DuncanS. That was just what I needed.
Further to this, on my dashboard, MYOB is keeping a tally of GST collected and paid - way beyond anything I actually owe the tax office. This is because every time I enter my BAS, I enter the amount I am paying as an "Other Liability" called GST Collected, and the amount I am owed by the ATO as an "Other Liability" called GST Paid. So I just keep on increasing my liabilities with every payment. Clearly a mess.
If MYOB knows my GST collected and paid, how do I complete the entries in the BAS to actually update the liability as I make/receive ATO payments?