How can I get my original hard drive back?

I got myself into a whole mess while trying to update my os system to Monterey from Mojave so I would really appreciate your help.

I'll try to make this as short as possible but basically I tried downloading and installing Monterey, it worked or so I thought, it successfully downloaded but installation failed because I realized I did not have enough space in my hard drive (my bad). I tried restarting and logging back in but all i got what like this banned symbol on the screen. I researched and saw that I had to install the last os I had which I guess is Mojave so I did but like the installation process never finalized either, like an error would come up. I tried again and same thing. So I tried restarting again and this time I was able to log in successfully and saw my old desktop and everything but upon attempting to use Finder to find and delete old things, nothing would show up and then I saw that my hard drive is now Macintosh HD - Data - Data - Data as opposed to the original one. And there's an additional one called Update but I'm not sure for which OS it's for. Either way I really would just like to have access to my original hard drive again but I'm not sure how to and I don't want get myself into an even deeper mess by trying to figure it out myself.

If someone knows I would really really appreciate your help. Thanks in advance.