Add remote upstream(or whatever) for forked repository:

git remote add upstream https://github.com/somerepo.git

Change remote url(f.e. in my case to use url with access token):

git remote set-url origin https://login:token@github.com/somerepo.git

Show default tracking info for local branches(git status shows it too if configured … your branch is up to date with …):

git branch -vv

Unset tracking info:

git branch --unset-upstream

Set tracking info:

git branch --set-upstream-to=origin/somebranch

Show tracking info for remote branches:

git remote show origin

Import branches from previously forked repo reffered as upstream into curren repo reffered as origin:

git fetch upstream
git checkout -b newbranch upstream/newbranch
git push -u origin newbranch