Hi. My name is***** you for your question and the opportunity to assist.
Can you tell me which version of Windows you are using?
You don't mention which version of Windows you are using but these instructions should work:
On your keyboard, hold down the Windows logo key (just to the left of the spacebar) and press R.
The Run box will open.
In the text area type: diskmgmt.msc and click OK.
In the Disk Management window, right-click on the F: drive and select "Change driver letter and paths"
click the Change button and use the drop-down arrow to select Z and click OK.
Click Yes to the warning and now the F: will become available to assign to your NAS drive.