When you apply for a job on JOIN, you may receive a message informing you that you already have an account and are therefore asked to use your password.
This happens if you have applied for another job in the past that was also hosted by JOIN.
What to do:
To apply for this new job, simply use the same password you used when you applied for your first job on JOIN.
In case you don't remember it:
Simply click the Reset your password link and follow the instructions. Once done, you will be returned to the job, where you can use your new password to proceed.