car and driver perk calculation

Hi all,

I want to make payment of Car hiring reimbursement through IT14. I also have to calculate the perk value for driver and car as it is company owned car. When I read nodes for Car and Conveyance in SPRO, it asks me for assignment of WT to allowance grouping. But Since I am paying the amount through and for different eligibilities I am maintaining IT589, I didnt make any allowance grpng for few reimbursements.

My issue is how system will now calculate the perk value? what is the solution to achieve this?

Thanks,

Megha