If you have lost access to email, there are many ways to reset the password using phpMyAdmin. Here are a couple of really simple ways to reset it.
XenForo not sending emails completely or emails aren’t delivered in members inbox? A step by step guide to verify your domain, create SMTP credentials and switch over to Amazon’s simple email services or SES in XenForo.
Forgot your XenForo password? Don’t worry. This step by step guide will show you how to recover a lost password in XenForo. Works for admins and members.
The complete visual guide to the position of each XenForo hook for header, footer as well as the forum_list, forum_view, thread_view and member_view pages
Usergroups in XenForo has permission set only for the front end (inline moderation, edit post, ban users etc) and provides no access to the admin area.