CRM mobile tasks not syncing properly

CRM mobile tasks not syncing properly

i have many tasks that show up in my iPhone app for Zoho CRM as not completed (e.g. not started, or in progress), yet they have all be correctly marked as complete in my online CRM instance.  how do i clear out all these old tasks from my CRM mobile app?  yes, I know that i can open each of them in mobile and mark them as completed, but there are hundreds!  besides this will over-write the correct completion date which is already in the online version for these tasks.

note, the problem may be related to the fact that some of these tasks were associated with leads that originally had different owners than me (and are now inactive on our acct).