Beginners have a 0.08 BTC wallet created by bitaddress.org. How can I exchange it for fiat currency?

The “Wallet ID” is specific to your Blockchain.com account and corresponds to that login. If you generated your address from bitaddress.org, you won’t have that address, instead you will need a Bitcoin address and a private key.

Here are the steps to get an external address from Blockchain.com support:

• To import a Bitcoin address from a third-party platform, click + Import Bitcoin Address and select an existing address generated outside of this wallet. Enter the private key of the Bitcoin address you want to import. Next, add a label for the address (optional) and select an existing sub-wallet to transfer funds to, or leave this blank to keep the funds in the address you imported. Click Import to complete the process.
• On the mobile app, tap the three horizontal lines in the top left corner to open the menu and select an address. Tap the + to the right of the imported address, then scan the QR code for your private key. Then give the address a name and press Save Name, or press No if you don’t want to give the address a name.

Anyway, once you have your Bitcoin address private key, you can import it into another wallet (you just need to know what format it is in).

Once you have obtained the address/private keys of your wallet, you can send your Bitcoin to an exchange and sell it for the currency of your choice.

You can find information about the private key format and how to obtain it here.

https://en.bitcoin.it/wiki/Private_key
https://en.bitcoin.it/wiki/How_to_import_private_keys