Skip schedule calls (about Maintenance plan)

After Tcode IP10, a schedule call is called, a maintenance order is created automatically. Now i want to cancel the maintenance order and also skip the schedule call. but the system says " the call can no longer skipped" and give the following message suggestion:

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Call can no longer be skipped

Message no. IP405

Diagnosis

You have tried to skip a date that has already been called.

System response

Since maintenance call objects, for example, maintenance orders, already exist for the dates that have been called, you can no longer skip a date within the scheduling process.

Procedure

If you do not want to perform the maintenance call objects due on that date, you must reverse the orders that have been called.

You can select the maintenance call objects that have been called using the list editing functions in maintenance processing.

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Although the above message seems giving enough detail, yet I just donot know how to reverse the orders that have been called. who can help me with detailed Tcode and button/path.

In short, firstly, how to reverse/cancel a maintenance orde. Secondly how to skip a schedule call which has been called.

Many thanks

George