Woocommerce to Xero How to Calculate a Donation

Hi,
I am using make to take invoices from woocommerce to xero. On each order I am donating $1 to charity and I am not sure how to get this to work.

Currently, the scenario is passing all line items, discounts, and shipping to xero. I guess I would need to take $1 off the total order amount and code it to donations in xero. What method would I need to use in make? Chatgpt said to use a calculation module before the create invoice in xero module but it was not very clear on the steps to get it to happen.

Any ideas?