Press the Fn + Esc keys to toggle Fn Lock
Enter BIOS/UEFI setup during startup
Open the Advanced or System Configuration menu
Find Function Key Behavior or Action Keys Mode
Change the setting to Function Key First or Multimedia Key First as needed
Save changes and exit BIOS/UEFI
Use Dell QuickSet or Dell Power Manager if available
Check the keyboard for a dedicated Fn Lock key
Update the keyboard or chipset driver if the setting is missing