To add a new user to AttendanceBot you need to first add that user as a member of the MS Teams Team where the bot is installed. If you're a team owner in MS Teams, you can add someone to a team. If you're not a team owner, you can submit a request and the team owner can then accept or deny it.
Step 1: If you're a team owner, go to the team name in the teams list and click More options More options button > Add member.
Step 2: Start by typing a name, distribution list, security group, or a Microsoft 365 group. You can also add people outside your org as guests by typing their email addresses.
Step 3: When you're done adding members, select Add. You can make someone a team owner by selecting the down arrow next to Member.
Step 4: Select Close. People that you add to a team will receive an email letting them know they are now a member and the team will appear in their teams list.
Once done AttendanceBot will acquire that new user & then the team admin can introduce him to the bot from the People >> Invite page of the settings panel. Here's a screenshot of the settings panel for your reference.