Hoe to set parameter id for screen field

Hai guru's,

i want to set a parameter id for screen field which exists on BD87 transaction, i know that if dataelement contains parameter id (example vbeln has parameter id 'AUN' and we can pass parameter value as

SET PARAMETER ID 'AUN' FIELD FIELD-VAL.),If a data element does not contain parameter id how to set that...

if any of you people overcome this kind of problem, plz reply to this query.

thanks in advance

innu.