Auto Populating a Related field for it to match the Related field on parent record

Hi All,

I am currently attempting to auto populate a related field on a newly created record, so that it matches the value in the field on the parent record.

The scenario is within Opportunities I have a field created via a one to many relationship on a custom module. When I then create a quote from the sub panel, I am trying to get this value to also pull through to the same kind of field (One to Many) on the quote record to match that of the opportunity.

I have found a few articles but haven't found anything that is around auto-populating a relate field that is created via a One to Many relationship.

Any help would be appreciated.