You’re seeing the missing Add button because the system doesn’t have the right permission enabled.
To resolve this turn on the WKROLETYPES system function, which allows workers to add worker roles within the configuration tool:
Log into Mosaic.
Click on Tools.
From the drop list, click on Configuration tools.
Now click on Permissions.
Worker role type permissions screen will show, click on add new role type icon
On the General tap, enter the required information.
Select the System functions tab.
Type WKROLETYPES in the search field.
Tick the Enable field.
Click Save.