This is generally easy to do as it goes in behind the railing system of the garage door opener.
Homemade roll up garage door opener.
A properly balanced garage door is less likely to crush someone or something and keeps your door opener from working too hard.
To know how to balance a garage door first disengage the opener from the door by pulling the opener release handle see opening photo.
This was done because i was informed by the garage door company that it was not a way to add a garage door opener to my doors but here is the evidence.
Then lower the door about halfway.