@Bhanuka Perera ,

Part serial current position is unallocated when the operational status of part serial is Scrapped, Planned for Operation, or Renamed.

In you case the serial is renamed. if you want to change the current position , then you need to go to renamed serial and rename it back to original serial no ( which is in your screenshot). You can find the renamed to serial no in serial history. 

Please make the serial part is in stock while renaming.

Regards,

Mithun K V