Entity Form - Pre-populate a field from a different entity.

Hi experts,

I want to pre-populate a field on the Create case entity form. This field(baseproduct) is an option set field in Account Detail entity.

There is a same field created in Case entity with same option set values.

Now, whenever the Create case form is loaded, base product field should be pre-populated with the option set value that is set on Account Detail entity. If there is no base product on the account detail record then no base product is populated. 

I assume it it to do with relationship mapping but not able to achieve this. 
Please let me know if you need any more clarification. 

Regards,
SdDev