How to withdraw GRIN from your pool? GRIN does not have wallet addresses, yet you ask for one in order to request a payout!
Right now you still can't withdraw GRIN yet until the first block is mature at around 17:00 UTC today.
Please note that the balance will be accumulated in your f2pool account until the wallet address is set.
If you wish to withdraw after the first block is mature, the fastest way is to get a wallet address from exchange such as Galleon or Bitmesh and set the address in your f2pool account.