If you are using debug_mode and have access to the console, it is probably easier to use the Explorer to fix this, rather than editing a save file.
Open the console, write 'explorer', then click enter.
Then this will show up. Click on "Achievements", and in the drop down menu find "Provinces".
Next, we'll find the specific province. In the search key we put in "Ambrakia", finding the province in question.
Click on the search result for the Ambrakia to open a new explorer window.
It should look like this. Inside the "Effect" part, we will be able to write Script that directly affects the province. If we want to remove a building, we will just write 'remove_building_level = <name_of_building>'. So in this specific case 'remove_building_level = military_building', then click 'Run'. This is pretty much how we quickly do stuff in-game when we work on the game and need to test something.
Open the console, write 'explorer', then click enter.

Then this will show up. Click on "Achievements", and in the drop down menu find "Provinces".

Next, we'll find the specific province. In the search key we put in "Ambrakia", finding the province in question.
Click on the search result for the Ambrakia to open a new explorer window.

It should look like this. Inside the "Effect" part, we will be able to write Script that directly affects the province. If we want to remove a building, we will just write 'remove_building_level = <name_of_building>'. So in this specific case 'remove_building_level = military_building', then click 'Run'. This is pretty much how we quickly do stuff in-game when we work on the game and need to test something.