Why does my computer have 1TB storage but can’t access it?

A couple years ago I bought a laptop (Thinkpad Yoga 14) and followed a professor’s tutorial to change its system from Windows to Ubuntu for class. After I changed majors, I tried to change it back to Windows on my own and sort of (badly) managed to do so. However, I messed up and I can’t access the majority of my laptop’s storage. It originally had 1TB.

Can anyone help me access the rest of it?

I don’t have any important information on this laptop, so I wouldn’t mind having to do anything that would normally cause any loss of data.