If you're having issues signing into the Do IT site, first make sure that you're signing in with the right email address (when you first signed up with us, you would have been sent a confirmation email to the address you used to create your account).
The error 'Invalid credentials supplied' will show if either the email address or password is incorrect. If you're absolutely sure the email address you're using to sign in with is correct, click on 'Forgotten password'.
Here, enter the email address for your account, and click 'Reset password'. If we can find a valid account under that email address, we'll send a password reset email out to that account. To complete resetting your password, follow the steps as they appear in that email.
If you aren't receiving that password reset email from ourselves, it's likely our email is being blocked by your email provider. Check your junk/spam folder first, but if our email is not appearing there do look to add firstname.lastname@example.org to your safe-sender/email whitelist (do contact your email provider/network administrator if you are unsure how to do this), then request a new password reset email.