Some time ago I have forked a repository B which is a fork of another repository A on github.
Let's assume, that my forked repository is C.
Now I wanted to contribute directly to repository A.
Therefore I wanted to fork repository A, but instead of creating a new fork (e.g. D), github brings me to my previously created repository C.
I don't want to delete repository C, but I need to start working on my new changes related directly to A.
How can I do it?
Update
I have found a very similar question: How can I fork the original repo when I've already forked a different fork.
However I have a problem which is not answered in answers to the above question.
The "intermediate fork" - B does not contain all branches from the original A. Assuming, that I keep working on C and just create a new branch, I don't know how could I base my new branch on a branch of A which is not included in B?