Just created an account as well, I am also having this issue.

Just found an old forum post that answered the same question! Worked for me, here's the link: https://support.box.com/hc/en-us/community/posts/29570925459475-Change-password 

Hi Rob,

Welcome to Box Community and glad to assist! 

To create a password for your Box account, please follow this process:

1. Visit https://app.box.com/reset and enter the email address associated with your Box account.


2. Check your email, you will receive an email with a link to reset your password.

• 
  
  • Password reset links sent via email expire 3 hours after they are sent. If you need a new link after your current one has expired, visit https://app.box.com/reset to have another link emailed to you.
  
  
  • If you do not receive an email from Box for this password reset, check to see if your Box account is associated with that specific email address or another email address.
  
  
  • Also, check your spam folder in your email client for this email.
  
  

Thanks for posting!