The quickest way would be to download the WD Drive Utilities program, install it, run it, plug in your Passport and format it, which should restore it to it’s full capacity. If that doesn’t work, you will need to use Windows Disk Management to manually delete the existing 32 GB ESD-USB partition and create a new NTFS formatted partition that utilizes the entire drive. Important: If you have personal files already on the 32 GB partition, they will be deleted when you format and/or re-partition the drive, so remember to back them up.
As for your files that were on the drive before using the Windows 10 Media Creation Tool, they cannot be restored. The Windows 10 Media Creation Tool should have provided you with a warning stating that the selected drive will be erased.