How do I add a canon dynasty to the dynamic coa system?

I'm trying to add House Paege of Fairmarket into the dynamic coa system. I'm familiar with editing things like localization files with Notepad++, but my knowledge is very limited. The biggest hurdle for me right now is the TGA files. I've been trying to follow a reddit post that Blackninja responded to a couple years ago (https://old.reddit.com/r/CK2GameOfthrones/comments/6cietf/how_do_i_add_a_dynasty_to_dynamic_coa/) but I hit a brick wall on step 2 about creating a tga file or using one that already exists and adding it to your dynasty. I downloaded something called Paint.net that lets you view TGA files, but I don't think I can edit them or take any one specific file. I know I'm doing something wrong, I just don't know how to get over this hurdle. There aren't a lot of posts about this stuff and there certainly haven't been any YouTube tutorials about how to do this, so any help, advice, and recommendations would be greatly appreciated.