All Helium Wallets will need to be migrated to the Solana blockchain. Please refer to the wallet migration guide about the different Wallets and what can be expected as part of the blockchain migration
12-Word And 24-Word Seed Phrases
When a Helium Wallet is created with the Helium Wallet app or Helium Hotspot App, a 24-word “Seed Phrase” is generated.
Users who created their Helium Wallet using the Helium Hotspot App will have a 12-word seed phrase, while the Helium Wallet app accepts 12-word seed phrases, all new wallets are created with 24-word seed phrases.
Read more about Helium Wallet seed phrases here.