Hi kiwistu,
Thank you for your post, and welcome to the Community Forum!
I understand that you're looking to file a late GST claim in MYOB, and to help you, you'll need to check if the transaction meant to calculate GST is already amended because changes to the transaction from the previous GST period will be automatically calculated as part of the claims. For more information, please refer to this Help article: Completing your GST Return.
Feel free to create a new post if you need further assistance.
If my response has answered your inquiry, please click "Accept as Solution" to help other users find this information.
Cheers,
Princess