Hi, I haven't logged in in years and I'd like to change the email on this account but I lost access to it a while ago.
https://forums.steamrep.com/account/contact-details You should be able to punch a new address in being you are logged in already and change it - then it will ask you to confirm to that new email. I believe that is its function.
It says this: Your email cannot be changed while your account does not have a password. Request a password be emailed to you
I'm afraid you will have to recover your email you created in order to get a notice from here to that email to change it.
I seem to have the same issue regarding the email and password. The email registered to my SteamRep account, I deactivated almost a year ago, as I saw the need to migrate to a new email address. I wish there was a way around this, but at the end of the day that was mistake/responsibility.