Train My GPTs Properly using external sources

I have created a couple of “My GPTs” that have helped a lot in creating content as the voice that we have in different companies, with our opinions and point of views. What I am missing is a way to train them with our blogs, not to be copying and pasting, or generating a word for each one of the posts.

Has anyone done this training of your GPTs properly that does not require too much human intervention ? I have several years of podcasts, blogs, etc. that i would love to use.