export the seed phrase and write it down or print it out. Keep it somewhere safe. If you happen to lose your phone or your computer breaks, you can use that seed phrase to recover the wallet. You can import it back into bither unter Import Private Key. There should be an option to import from a HD Account phrase. You use that and you will have access to all of your bitcoin again.
Thanks for knightdk's help on answering this question,
Yes, users can backup the HD seed phrase or HD seed QR-Code, and can import to Bither when they want to recover the HD Account.