Go to the Setting tab and select Manage Wallets.
Choose the wallet you want to back up, swipe left, and select Edit
In the Edit Wallets screen, press Show Backup Phrase.
You have 3 backup options:
1) Keystore file
2) Private Key
3) Mnemonic seed phrase.
You only need to use one option, but it is recommended to back up using all three. Save your backup safely and NEVER share it with anyone.
* Note: If you did not import the Mnemonic seed phrase when importing a wallet, you can not export it, only Keystore and Private key will be available.