First of all, to get the credentials needed to access the bookingpad webapp for other agents you must be a superagent ( this means your credentials allow you to make changes and view more information than an agent)
You will know if you are a superagent or not because superagents have been granted access to the agency portal.
If you are not allowed to access the agency portal but you are in charge of adding more agents to the web app, please ask your manager or the person who sent you the bookingpad invite to change your status to superagent.
And then follow the instructions in this link.
If you are indeed a superagent you can add more agents by going to the agency portal and following the instruction in this link.