Hello @gmtzb. As @Geert said the rewards are minted on the Stellar Network, not on the Polkadot network (yet). There is a bridge which allows you to move TFT’s between the two. You should. Anyway this might be too much information and confuse you more than it helps you.
Here’s what you do: go to http://portal.grid.tf
. The portal should be able to access your polkadot key(s) and present you with the available accounts. Select the account you have created you farm in.

If you clock on twin in the right hand side bar, you should see what you see
. The address is you stellar wallet address you have provided to the farm. This is where your reward has been sent to after being minted at the end of the proof of capacity period.
You can look up the balance here. Top left of the page is the search box - if you paste the wallet address there you will see you balance.