I'm glad you found a solution. "You need to read (the documentation) more" and "Read the manual" are not upsetting statements, they are plain facts. The disconnect was between the words you were using to think about the problems and the words the community uses to describe those concepts.
When we encounter an obstacle, we can either choose to learn or complain how difficult it is for us. On a personal note, I struggle with this a lot myself too. We cannot expect people to coddle us, especially in a professional setting.
bcftools is the go to for me in such cases.
a bit more details would be much appreciated, as I studied it, but without any success.
You need to study and experiment with it more, then. It's a pretty straightforward tool.
I've edited my answer above