http://sparrowa7io5pz6ud3ehqzosvepbxbxt2zphmkjsylp2zgxooko23pqd.onion/docs/faq.html
Your existing address labels will even be applied to the new addresses, since Sparrow has no way of telling the passphrase has changed.
Further, your wallet will show no funds are present. They are not lost however. To fix this, close the wallet and reopen it, entering the passphrase carefully.