This article explains how can new Linguist users create their own password (when the log in the first time and didn't receive any password from their Project managers) or how can any user reset their password in case they forgot it.
An example of a forgotten password and a link to reset it.
Just follow this "Forgot your password?" link and fill out your username. The password recovery instructions will be sent to the email address connected to your username. Click on the link in the email, fill out your new password and submit it.
Now you should be able to log in to your account.