1
If your USB drive is encrypted with Bitlocker, the only place the Bitlocker Recovery key is automatically stored is on the associated Microsoft account on the link below.
https://account.microsoft.com/devices/recoverykey
2
If you are unable to find the Bitlocker Recovery Key on your Microsoft account and cannot access the USB, if there is no problem loosing the files on the USB:
Please Note, this process will delete all data on the USB.
Right click your Start Button and open Disk Management.
In the bottom pane of Disk Management, right click the partition on the USB drive and select' Delete Volume'.
That will result in the USB being marked as 'Unallocated Space', right click that and select 'New - Simple Volume' and accept the defaults.