Empty list for Units field when creating new survey in Collect

Dear Jinkai,
The set of predefined list is created automatically every time you create a new survey and it's accessible from the Survey tab in the survey editor:

Then you can specify which ones of these units of measurements can be applied for the attributes in your survey by defining a list of units in the Numeric Attribute editor:

Just click on the small green plus button and start to add units to your list:

You can use the predefined units or create new ones if you need.
Many thanks,
Open Foris Team