First thing to check into is whether or not as a reseller there is a form you can provide to the vendor so youo can buy FET free. There is such a thing for sales tax, called a resellers permit.
In QBO all you can do is create a service item that posts to an FET liability account you set up. When required, run a liability report and find the total FET due for that reporting period and pay the tax. Use that service item on the sale document to the cusotmer.
IF you have to pay the FET even as a reseller, then that FET is part of the cost of the tire