You have to release the pressure of the thread being caught up so tight. I would start cutting it into pieces. Use anything that will let you release it, razor blade, thread ripper or a pair of small scissors with those very sharp tips. Then use a small vacuum or tweezer's to get all the small pieces out of the mechanism. When I have had to do this, I have hade to take the whole bobbin assembly apart. Even a small piece of thread can cause you more problems.
Wonder why it happened in the first place? Are you using the correct bobbins? I have several different machines and have learned the value of buying machines that use the same bobbins. Some that look the same have a tiny size difference that can cause a lot of problems. Maybe a longer piece of thread that wasn't on the bobbin got down there and snarled itself up. Hope this is a one time problem and your sewing becomes much happier today.
Edited to add: I just realized you said a Sweet 16. I think what I have stated still applies, but maybe not. I have a Nolting long arm and when I have had bobbin problems it has been because the bobbins were wound loosely. Rarely do I see thread snarled down there. Good luck with clearing your problem up.
Last edited by Barb in Louisiana; 03-19-2019 at 05:27 AM.