How do I get my onchain bitcoin on my ledger or trezor onto the lightning network?

Easiest: Use a custodial service such as Strike, or Coinos or Wallet of Satoshi.

Each way is similar, this example uses Strike;

1. Install the Strike app for Android or iOS
2. Tap on receive
3. Copy the Bitcoin address or scan the address QR code with your onchain Bitcoin wallet.
4. Pay some Bitcoin to this address.
5. Wait for the transaction to confirm on the blockchain.
6. The Bitcoin in your strike wallet is now ready to send over the lightning network

How do I get my Lightning Bitcoin into my onchain wallet, such as cold storage, ledger or trezor?

Easiest: Use a custodial service such as Strike, or Coinos or Wallet of Satoshi

Each way is similar, this example uses Strike;

1. Install the Strike app for Android or iOS
2. Tap on receive
3. Copy the Lightning address, or lightning invoice (looks like an email address).
4. Pay this lightning invoice or pay to this lightning address.
5. When funds have arrived, go to send.
6. Enter the onchain Bitcoin address, and choose your fee rate, fast (expensive), medium (economical) or slow (free).