If you selected the wrong GST rate for a transaction, to edit the GST rate after saving the invoice, you need to follow the below steps:
Step 1: Go to Transactions, then select voucher, then select Modify.
Step 2: then put the voucher number for which you have selected the wrong GST rate for a transaction, then press OK and F2 to load the voucher.
Step 3: Make the changes to which you have selected the wrong GST rate for a transaction. For this, you have to check the sales type, bill number, and item tax rate.