By default recovery is disabled. To enable the recovery, change the value of the property abpm.transaction.recovery.enable from no to yes. To know how to change the property, refer the Updating System Properties section of the Admin Guide.
If Queue Processor is enabled, Queue Processor does the recovery. The property abpm.transaction.recovery.enable will not have any effect on recovery process. Queue processor tracks all the jobs (request for execution of process flows). If jobs are not completed in previous run, then queue processor will recover them automatically. To know more about Queue Processor, refer to the section Load Management.