Hi @T.BASK 

1. All Tools - which are setup as Serialised , can follow the below process.
2. Raise a Fault report/Corrective Maintenance WO , on the parent object on which this tool is connected. ( You may raise it directly on the Serial Object as well, depending on your data setup)
3. Use the Returns tab in the work order , to return the faulty / unserviceable tool / Non calibrated tool ( depending on the issue) , to the inventory
4. Create a Purchase Requisition in the Work Order ( Optional )  , for the Tool Part and serial number as an External Repair case . Enter the External Service code ( Calibration, Repair, etc ) 
   1. For Functional Objects, use NO PART LINES, create a normal service request for servicing. You cannot follow order code 6 - repair external - process for Non serialised Functional objects. You just purchase the service from the Vendor. Cannot get tracking for Non serialised Tools.
5. Process the Order code 6 Purchase Order (PO) - Repair External - and release the PO , with the Tool Serial
6. A Customer  order connected to this PO, will be raised . Use this customer order, to reserve the Tool serial number from Inventory and dispatch to the customer with the Delivery Note
7. Use the PO connected to this customer order (CO) to receive the Serialised tool, when it is dispatched by the Vendor

Regards

Vivek 

Thank you @VivekBhandiwad  I will try when i have the acces to Create a Requisition.

I don’t have access yep …