How do you add a logo to a trademarked wordmark?
I don't understand the question.
A trademark is a logo that has been registered as such. There are entities that solve this for you, google for register trademark and you'll find solutions.
A wordmark is actually a logo that's made out of text. Such as the new microsoft logo. Or, if you look at https://pftoday.com, the logo you see is also a wordmark.
So, what you do actually want to achieve? Do you want to add some graphic to the existing logo you have? Or trademark it?