To add options to the drop down lists:
Navigate to the Administration page.
Under the Developer Tools section select Dropdown Editor.
Select the Dropdown list you wish to edited by looking for its name.
Add new options by filling out the name and display fields at the bottom.
Click save.
If you do not know the name of the dropdown list then you can find it by finding the field using it within studio
To add a default select follow the below steps
Return to the field settings that the dropdown is assigned to
Select the required value from the Default Value dropdown
If the field also has a dependency of a Parent Dropdown, you will be required to specify which option it falls under. Do the following:
Next to Parent Dropdown, select the Edit Visibility button
Under the Available Options section, you will see the list of options. Drag the new ones to the relevant option from the parent dropdown