Thank you for the responses. I tried creating the business rule on the primary table and using the GlideRecord on secondary table in the script section. I am now able to insert new records on the secondary table. 

However, it is not showing me the correct related values in the secondary table records. 

For instance, I have the following fields in the secondary table - 

1. Related Project Number
2. Related Project Name
3. Instance Version

These values are to be populated from the primary table (the respective project number and names and instance version values)

I can only see the project number in both the name and instance version fields though. PFA screenshot for reference. 

Note: The instance version field is a choice list in the primary table. I just want to show the data (not necessarily as a choice list) in the secondary table, i.e. for the Project Number 123 & Project Name ABC, the instance version is XYZ. 

Thanks!