I have follewed the steps listed below:
To set predefined field values:

• Click the name of an action in the Buttons, Links, and Actions list or the Global Actions list.
• On the action detail page, click New in the Predefined Field Values list.
• Select the field you want to predefine a value for.
• Specify the value for the field.

However whne I click NEW

There is no option listed to choose.
Click Save.
 

When I first tried this challenge I was not successful and was having a difficult time trying to figure out what I was doing wrong. The error I received when checking the challenge was:
 
I was thrown off becuase one of the criteria for the challenge is:

• The custom button must be named 'Google Link'.

But "Google Link" is not a valid name. I believe this shiould instead state that the *label* should be "Google Link". Ultimately I passed the challenge once I realized that I had created a link instead of a button.