Head to this page and from there you can enter your email to trigger a reset link to be sent. (That email will also include your unique username, which needs to be entered on our login screen after resetting.)
If you're not getting a reset email at all, we suggest that you try adding robot@letterboxd.com to your email contacts, in order to increase the likelihood that you receive our automated emails. Some email companies like @att, @hotmail, and other internet provider domains have trouble getting our emails. If that doesn't help and you can't find anything in spam or junk, we can try changing the email on your account to an alternate address.
It's also possible that your account is connected to a totally separate email, in which case reach out to our support team with details.