Hi, I am Dave, I will help you with this.
If you cannot find the Bitlocker key, the data on that drive will not be accessible and re-installing Windows will result in loss of all data on the drive.
You need to delete app partitions on the drive to remove Bitlocker.
At the very start of the Installation Process, press Shift + F10, or Shift + Fn + F10 to open Command Prompt
Run this command and hit Enter:
diskpart
Run this command and hit Enter:
list disk
(Make note of the disk number you want to convert and enter it into the next command - replace X)
Run this command and hit Enter:
select disk X
Run this command and hit Enter:
clean
Then close Command Prompt and restart the installation.