How to replace modify ICONS
Hi
Please be specific about what you want
What icon ??
Which icon ???
ERPNext / Frappe Version ??
Frappe Version icons
A picture would be nice !! 
Want to change the icon
Which icon set do you want to use ??
both octicons and fontawsome are available by default in Frappe
Want to change both icon sets
Want to change the default icon sets
These icon file are hard coded into the core at lots of places… in this file …/apps/frappe/frappe/public/icons/timeless/symbol-defs.svg
You could probably add additional icons to the above file like how its done here
When that is done just do
bench build
and
bench clear-cache
You should able to select you icons.
However do note unless its in a separate app it will break when you update your ERPNext / Frappe
I also just find, thank you!