You should add the original repository from TA in git remote. You may check with
git remote -v. Then, it will show something like this:
origin git@gitlab.cs.washington.edu:syhan/16sp_cse451_os161.git (fetch)
origin git@gitlab.cs.washington.edu:syhan/16sp_cse451_os161.git (push)
upstream git@gitlab.cs.washington.edu:syslab/16sp_cse451_os161.git (fetch)
upstream git@gitlab.cs.washington.edu:syslab/16sp_cse451_os161.git (push)
If you don't have one with
syslab/16sp_.. you should add it by
git remote add upstream git@gitlab.cs.washington.edu:syslab/16sp_cse451_os161.git
With this, you can pull from the repository to merge onto your code by
git pull upstream master