Whenever you need to add Mobile respondents to your account, simply go to Manage Mobile Team module and add mobile respondents (AKA Field agent).
You can create mobile teams (made of several mobile respondents) so you can easily publish mobile forms to one or more team, then collect results for a specific team, geographical area or else.
In case you want to provide access to the Datafield platform to one of your field agent, simply grant admin right for a given period and time so he can view survey, launch mobile campaign and view the results.
Here is a 2-steps tutorial to learn how to add one single agent to your team:
If you need add lots of field workers, you can easily add them all in bulk. See the tutorial here.