If you or a colleague has moved sites, the access permissions in the user account will need to be changed so they can log in to the right location or site.
Only Admins & Managers can edit user details - if you don't know who that is just drop Trail support a note and we can help you.
Here's some more on Roles & Permissions and Managing Users
To change a user's access settings, edit them from the Users page.
Here you can edit the role:
You can also edit the site access of a user to assign them to a site or group/area:
If it's a different person (eg. a new member of staff) it's better to create a new account for them.