When setting up a Helium wallet through the app, you are prompted to write down the 12 words seed phrase. These are the mnemonic phrase generated from the private key of your wallet, and the only way to access the wallet.
The 12 words can never be recovered if they are lost, and they are the sole key to accessing your wallet, the HNT it contains, and all access to your Hotspot and it’s rewards. Lose the 12 words, lose it all. You’re not able to log into your account without them, nor can you transfer HNT or a Hotspot to a different account without them.