How to rollback task

In my case, flowable is an single service. It depends on someone business service (like OA). If OA call complete(taskA) accidentally, how to rollabck to process from TaskB to taskA ( It may take some time to find out the problem).
In other words, are there any way to rollback to any finished tasks in an activity process instances?

Hi Denny,

You can’t rollback in the term of database rollback. (there is e.g. how to rollback external system call). What you can do is to move execution to the specific state with