Go to https://polkadot.js.org/extension/ & install the extension

Open the extension, press the “+” icon in the menu & either use your existing substrate wallet OR create a new one for the claim

Follow the dialog to import the key. In the end, you should see the address corresponding to your validator key. Use this address when claiming the tokens you have purchased during the public offering or if you are selected for the airdrop (Read the criteria here).