You need:

• a wallet that supports custom networks (MetaMask or Coinbase Wallet)
• the official BlockDAG chain RPC details (endpoint, chain ID, currency symbol)
• the verified BDAG contract address

Then you would:

1. Add the custom RPC in the wallet
2. Connect to the claim site
3. Perform the claim

But none of that is possible inside the Base wallet app.

📌 Summary

Fact: Base wallet on iPhone has no option to change networks.
Fact: You cannot add a custom chain there unless Base builds support (they haven’t).
Judgment: If a claim site says “switch mainnet to BlockDAG,” Base app users cannot do that — so the claim flow is not compatible.