The necessary BIOS settings are similar for all 3 docking stations. Please refer to the individual notes in the following instructions.

Reboot your system and press the F2 multiple times at the Dell logo. In the BIOS, proceed as follows:

NOTE: For some systems, the following settings are all found under the section USB-Configuration.
  1. Navigate to System Configuration and then to USB-Configuration.

  2. Select the options Enable USB Boot Support and Enable External USB Port.

  3. Navigate to Dell Type-C Dock Configuration and select Always Allow Dell Docks.

    NOTE: If you are using a D6000 Dock, this option must be disabled.

     

  4. Under System Configuration navigate to USB PowerShare and activate this option.

  5. Navigate to Thunderbolt Adapter Configuration, and select Enable Thunderbolt Technology Support, Enable Thunderbolt Adapter Boot Support and Enable Thunderbolt Adapter Pre-boot Modules.

  6. In the same category, select Security Level - No Security.

  7. Now navigate to POST Behavior and Fastboot. Select Thorough.

  8. On the bottom right click the Apply button to save the changes made. Exit the BIOS by clicking the Exit button.

NOTE: Please note that items 4 and 5 apply only to systems with Thunderbolt controllers. If this does not apply to your system, the options are greyed out or not available.

 

That will ensure you that have the latest updates on the system and ensure it's correctly configured for use general use. To address the Bitlocker query, I don't believe it's possible to have the Bitlocker prompt on the external screens pre Boot. I have a WD15 dock in front of me and I don't get video on my dual external displays until the system has logged into Windows. I believe that is a design limitation of USB-C technology.

Alan