I used the COH2 UI Asset Browser v2.0 by Janne252 find the icon and Export the icon and saved it in my C:\User\name\Documents\my Games\company of heroes 2\mods\tuning\data\ui in UI I added a new folder called portraits and saved it there then edit it and change it's name to "Icon_strategic_bombing_raid"
I did what was to said on the tutorial.
Add my icon ModIcons_mod I.D number_portraits_Icon_strategic_bombing_raid to my bombing abilities it wouldn't work it came out as a blank Icon every time I tried. So I deleted my edit icon and tried again without change it name.
So I just copied the icon name only "Icons_commander_cmdr_german_strategic_bombing" and added like this. Bombing ability\ui_info\Icon_name\Icons_commander_cmdr_german_strategic_bombing and it worked in game without adding the "ModIcons_mod I.D number_portraits" strange maybe it only works in units not abilities!
All icons can be changed, but there's one bug: The filename of custom icons must be lowercase.
The "Icons_commander_cmdr_german_strategic_bombing" is available in the game so you can indeed use it by calling this name directly (everything from the Asset browser is in the game available). The export isn't needed in this case.
If you would have made a change, then you have to save it in the ui folder. The "icon_name" in the tool would be "ModIcons_123_portraits_new_strategic_bombing". The file is called new_strategic_bombing.png in this example and saved in the map ui/portraits.