Assuming you mean how to backup a Coinbase wallet containing cryptocurrency, here are instructions provided by Coinbase:
“Backing up your wallet is important. If you lose your phone or buy a new one, you can restore your cryptocurrency by importing your key into a new wallet.
If you don’t backup your private key and lose it, you will lose access to your cryptocurrency.
To backup your wallet:
Open your Coinbase Wallet app
Tap Settings on the bottom of the screen
Tap Backup Wallet
Read the disclaimer and tap I understand. Proceed with caution.
Enter and verify your password
Your backup phrase will now be displayed. Write it down and store it in a safe place.
This is your only copy of this information. If you lose it, you will lose access to your cryptocurrency. Do not store it on Coinbase, Dropbox, Google Drive or other cloud storage services as these can be hacked.”.
Thus, it is very important to backup a Coinbase wallet containing cryptocurrency. By following the instructions above, one can ensure that their private key is secure and that they will not lose access to their coins.