Unable to set default value for Autocomplete

Hi there, 

I have a form that contains an autocomplete element whose value is selected by user when creating a new feature. Next time, when a user is editing this created feature, the selected value would be populated into the autocomplete. 

I tried to use set form element property activite for label or value, both unable to set value for autocomplete. 

any suggestion would be appreciated. 

kind regards,

Minbin