This is not such a complicated process. Many developers can help with this. Where it is more difficult to be free from developers further. I know since I ran into this myself. Later GTM helped me https://www.owox.com/blog/articles/custom-tags-in-gtm/. For example, it is now much easier for me to load banners, although earlier I asked for help to do this. So now you should contact the developers, and then you no longer need it.