At the left top of the MT4 platform.
Also, in Navigator / Accounts.
I think - nothing you can do in case you forgot account number and password.You can ask the broker but as far as I understand - the brokers are not keeping the passwords (they do not know passwords) ... but try with broker ...
You can always reset your account password in the client area of your broker website.
So, visit the website of your broker, locate your account and look for the reset account password option.