To access FirstAgenda in your organisation, you need to receive an invitation email from the organisation which has invited you.
If you have not received a welcome email, you should contact the FirstAgenda administrator in your organisation - or the person responsible for your team, as they are the only ones who can give you access to FirstAgenda.
Before you contact your administrator, it is a good idea to check that the welcome email has not been stopped by the spam filter of your email programme or is not to find in the "Junk" folder. This file can be found in the navigation window of your email programme. Also check the "Clutter" folder if you are using Outlook 2016 or later versions.