To add a new user to AttendanceBot you need to first add that user as a member of the Microsoft Teams Team where the bot is installed. If you're a team owner in MS Teams, you can add someone to a team directly. If you're not a team owner, you can still follow this process to submit a request which team owner can then accept or deny it.

Step 1: Go to the team name in the "your teams" list and click "more options" ellipses at the right. Select "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 be able to acquire that new user For more information about activating and/or inviting new users once added to Microsoft Teams, read this article.