{Dynamics 365 Portal} How to auto populate lookup on a create from a subgrid

Hi,

I have a web form which create the record for the 'Application' entity, I then have one more steps with a subgrid to the related child entity "Requests" i.e. 1 application can have more than 1 request. In this steps, I have added the metadata for the subgrid and added the create button which open the Entity Form for Create Request.

How would I pre populate the Application lookup on the qhile creating the Request record from the subgrid.