Erpnext - Letterhead is not updated according to selected Company

This happen when you create a new doctype and add new record, supposedly the letter head is link with company value like for example if company is selected as abc inc then letter head should also be abc inc. But in this case it does not automatically update and need special script to update manually. Any answers would be acceptable. If can give the RCA (Root Cause Analysis) would be great.

you can set letter head in your company

The letterhead is already created by project owners and when I select company when adding new record for doctype the letterhead is still same and not same with company.