Logging out is done via the settings screen in WFP Apps.
If there are pending sync items you are warned about it and given an option to cancel or proceed with sign-out. If there are no items pending sync then you will be signed out of the app.
PLEASE NOTE: If a user signs out whilst a sync is still in progress this will result in the sync not completing and as a result PDF reports will not be available for any jobs in progress.
Logging Out of Mobile Apps