How to charge/opt-in for bed sheets directly via booking.com?

Hi! Is it possible to set up a voluntary extra payment for bed sheets via booking.com, so that the guest can opt in and pay the extra fee if they'd like to have bed sheets and towels? I googled this and found a guidance to go to VAT/Tax/Charges or edit my Policies, if the option is not available there- but still can't find the option to edit this. Anyone here who has managed to do this and could tell how?