Lift the presser foot, turn your tension dial to its lowest setting and use a long pin to try to pick out the piece of debris from between the tension discs. If you can't get it, or can't find it you may need to have your sewing machine looked at by a professional. If you adjust your upper thread tension and it makes no difference, your tensions are probably not the problem. You may have another problem with your sewing machine. Since most problems show up in the thread, and that is what you see, you assume the tension is at fault.
Some manufacturers write it on their sewing machines as a selling feature.
You're not going to get top of the line technology in a bottom of the line sewing machine. Bobbin case tensions should be the LAST thing you should try to adjust. Bobbin Case Tension Bobbin thread tension should be the last thing you try to adjust. Check to make sure your bobbin case is threaded correctly. You should feel light thread tension when you pull the thread out of the bobbin case.