How to set From: in pjsip

Hi,
I need to change the INVITE part of the Header “From”:
From: sip:[email protected];tag=V1iErQloFE2120KjPz.kR6KTsFERy7jQ^M

To this shape:
From: “Testing” sip:[email protected];tag=V1iErQloFE2120KjPz.kR6KTsFERy7jQ^M

Where 519999999 is the hard codded value.
Thanks in advance

please check from_user