Huge unknown items on WD My Passport - help

On My Passport I have the C drive from my PC, (Win 10), and Drive H - the Passport, (500 gb). On Drive H are listed the backed up files from my PC and then “Other back ups”, 130 gb, and “Additional files”, 339 gb. My WD is almost swamped by the latter items. I am unable to identify them, do not know how to interrogate them, and fear that my only recourse may be to format the drive and start again. My technical knowledge is very limited in this area and I would be grateful if someone can explain what these mystery objects are and put me on the right path.

Hello Bellfield,

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