Multi forms on a single entity

Hi all,

I am using online 2016 version of CRM. I have Multiple forms developed, also a field on each form which is common (lets say A of type Lookup). I wrote a Java script for onchange value of A field, it will change redirect to the appropriate form based on the selected value. its working fine. Now I wanted to set a default value based on the  form that loads after changing the value in A field. Can somebody help me on this.

Thanks in Advance.