How to achieve dynamic value auto set on a field on project form through ATF

[Sardash]

 

I want to autoset logged in user on OBS Engineer field through ATF.  For this 

I have created a new user - OBS Engineer and i have impersonated with same user and tried to set this user as a reference via Set field values step but no luck. Can anyone help me achieve this through ATF. Right now i am getting a blank value and this field is a reference field

[Ankur Bawiskar]

@Sardash 

any ref qualifier on that field is restricting the user from being set?