Multiple value attribute in UserApplication workflow

UserApplication 4.0.1
I have one multiple valued attribute which need to be populated during the Initial user request form.

eg:
Attribute: trackID (Multi valued attribute)

I created a form with 2 fields in my request form

From Field name | Data Type |Control Type |
trackID | String | Text
TrackID2 | String | Text


In the Create Entity data mapping.

I can only point one form feild to "trackID" Attribute

Modify type | Modify value expression | Traget Attribute
Replace All | Flowdata.get("Start/request_form/trackID") | trackID


How can i populate my two form field entries to trackID attribute?