For those wondering, I believe you just need to buy an additional part of the outfit to receive the add-on. This can be done by selecting the 'Farmer's Outfit' option under the 'Rewards' tab of the reward interface.
It might be worth checking Diango's storage (which you can access through your bank), as you may have received and destroyed the prize before. If you have, he will hold onto it for you.
27-Dec-2020 12:32:52