Hi Linlin12, not sure about your problem if you either do not know how to login or if you just forgot your password. If you in general want to know how to use Sync for IOS please refert to https://support.mozilla.org/en-US/kb/sync-firefox-bookmarks-and-browsing-history-iOS In case you have lost your password please have a look into https://support.mozilla.org/en-US/kb/ive-lost-my-firefox-sync-account-information In case my understanding is wrong please don't hesitate to give more details.