The need to modify the purchase Bill occurs when the user needs to make any changes in the Bill/Invoice, like in case the product tax rate needs to be changed or a wrong bill amount has been entered. With this option, users can change the tax rate of a particular product.
After creating a purchase invoice, if users want to change the tax rate on their products, they can do it. Make sure you update the vendor's GST number in the software.
The shortcut key for using the Change Tax Type option is "Ctrl+F". After opening the purchase invoice, press Ctrl+F to open the Change Tax Type window.