To add another user, you just need to access the Users page.
Once there, you just need to click on the "Invite Users" button and type in the chat bubble the name and email address of the user you wish to invite.
The users you invite will soon receive an invitation email with an activation link.
To be able to access Claimable, they just need to follow the link and set up a password.
Please remember that for security reasons the activation link in the email will expire after 48 hours.