Automatically Associating Account to Agreement - Salesforce

Hi there,

In Salesforce, when generating an agreement from an opportunity I can get it to automatically associate with the Opportunity and the Contact, but I can't seem to find where to associate it with the Account as well. 

Ideally we would like to have it where the rep clicks "Send for Signature" and it automatically populates Account, Opportunity and Contact.

Thanks in advance!