Which sent contact requests are withdrawn?
Every request you sent that is still pending on XING and older than the period you choose. Newer requests stay in place, and so does any request to a profile in an active follow-up sequence. Because pending requests count against your XING limit, this frees up room for new ones. XING limits and ZingBot explains how XING’s limits work.
Open the contact requests page

Contact Requests lists the requests you have sent on XING that are still pending. They count against your XING limit even if they are never answered. One prerequisite: your XING credentials must be stored, or the cleanup button stays disabled.
Choose the age threshold

You decide how old a request has to be before it counts as old. ZingBot withdraws older pending requests; newer ones stay.
Start the cleanup

ZingBot now works through the requests inside your XING account. It takes a few minutes; you can leave the page open. While the run is in progress, the button is disabled.
Done

When the button is active again, the run has finished. The old requests are withdrawn; newer ones and those to profiles in active follow-up sequences are still there.
If cleanup will not start
The button is disabled in two cases: while a workflow is running (wait for it to finish), and when your XING credentials are missing in ZingBot (store them and try again). If a run keeps stopping, contact ZingBot support.
A request was not withdrawn
Then it is newer than the period you chose, or the profile is in an active follow-up sequence. Both are intended. Choose a shorter period if you want younger requests gone too.
Delete a contact or a message?
Contact Cleanup cannot do that: it only withdraws pending requests you sent. Delete existing XING contacts and messages directly in XING; the steps are in XING Help.