If you use a paper sign in sheet or need to manually add participants, no problem!
You can manually add meeting attendees on the Meetings & Offline tab after your meeting.
Find your meeting under Meetings & Events, and click the Attending or Attended (if the event has past) button.
Next, click the Add people button to upload a list or manually add individuals:
If you have a.CSV or .XLSX list of your attendees, you can upload it here and click Upload.
If not, fill out the data fields for each individual you'd like to add and click the Add Person button.
Click anywhere outside of the Add Meeting Participants window to return to the meeting tab.