Before claiming UNI, you have to login to your Metamask in your browser. If your Metamask is connected, then you can login by password but if you don't have access in your Metamask, you need to have private key or Memoric pharase. If you lost PK or Memoric pharase, we are sorry, you will lost everything in that wallet. If all are ok, then you have to connect metamask with Uniswap and claim your UNI. So you need to have ETH in your wallet for gas fees.