The thing to bear in mind with the envelopes function is that it employs the Envelope Address and Envelope Return styles from the template the current document is created from. If you have these sttles in your document template and your normal template, the document template definitions will take precedence.
The basic principles are covered at
http://www.gmayor.com/changing_envelope_layout.htm which was mentioned earlier in the thread. This works for all versions up to and including Word 2016, although the illustrations are mainly from Word 2010.
Having made the changes ensure that the document template is saved or you will be back to square one next time.
If all else fails, use a template - see
http://www.gmayor.com/Envelope_Label_Add_In.htm which comes with a pre-prepared #10 envelope template.