SD Rebate Condition configuration

Dear Expart,

How can i update or set up rebate condition for below requirments:

if customer get achieve sales qty more than target qty, then customer will get 1 taka for extra achieve qty.

target qty = 100, customer achieve qty = 105 then customer will get (5 * 1) = 5 taka

thanks

Md. Enayet Hossain