Set changeable default value to Field

Hi All,

I have one issue.

I have field XXXXX in assignment block in web ui,

This assignment block is Table view,

My issue is ,

I need to set default value "Insert value " for field XXXXX.

When i enter the data for this field,The default value should be remove.

Means i need to set changeable default value for field XXXXX.

Please help me how to solve this issue?

Thanks & Regards

Nitin