If you still have the accounts saved within the RuneMate client, but have forgotten the passwords/emails, you can recover them by doing the following:
Open RuneMate
Open OSRS
Start a bot (any will do), selecting one of your accounts saved within the RuneMate client
The bot will start entering the email address in the "Username" field in the OSRS client
Note down what the email address is
Right when the bot finishes typing the email address, and before it starts typing the password in to the password field, click on the username field again, and RuneMate will type your password in to the "Username" field, instead of the password one (since you clicked on the username field)
Quickly note down what the password was (or repeat the above steps if you missed seeing it in full), as once RuneMate finishes typing your password and realises it did so in the username field, it will automatically begin backspacing to delete it and it will then start typing it in the password field as XXXXX