We have some repositories, that are just slight variations on a previous done work. As such, we created them by forking the repository that has similar code that will be used as a starting point. However, since it is a fork, each time in the new repo we open a PR, by default it will do it towards the original repository, instead of remaining inside the repo.
The fork was basically only intended to create a copy, there is no point in keeping them linked or even in sync. The two repositories, old and new, should be able to behave independently from each other.
However, I find no option to sever the link between the both repositories, nor do I find a setting that allows me to select the preferred target for the PR, so I can put it to the current repository.