Your tensioner may need to be taken apart or at least re-set to a lower number. Your manual should show you how to do this.
Just ignore the numbers to whatever extent you can - some tensioners stop turning when they get to the lowest number, so that would require re-setting the tensioner. If your tensioner turns past the lowest number (0 or 1) just ignore the number it's on and use the quality of the stitches to determine the proper setting.
It would be very difficult to damage the tensioner, so don't worry. The check spring is the most fragile part and it's difficult enough to break those.
Following the manual, raise the presser foot and thread the machine. Use a different color in the bobbin than in the needle and use a fabric that doesn't blend with either of those colors to make your test runs.
Sew a few inches and examine the stitches, top and bottom. If the bobbin thread is coming up to the top and your upper tension is already as low as it will go and your fabric is not puckered, adjust the bobbin tension higher by one or two complete clockwise turns of the adjustment screw.
Test again. Is the bobbin thread still showing on the top? If so and the fabric is still not puckered, turn the screw another full turn clockwise. Repeat until the fabric begins to pucker. At that point, turn the screw counterclockwise until the fabric is no longer puckering.
Now, do you have a nice seam on both sides, with distinct firm stitches in the needle thread and in the bobbin thread? Chances are, you have wads of thread on the underside of the seam. If so, turn the needle thread tension to a higher number and test again. Repeat until you are getting a nice even stitch on both sides of the seam - the needle and bobbin threads.
Always thread the machine with the presser foot up and do your testing with a straight stitch foot and the feed dogs operating. The settings that are working for normal sewing will be close to the settings that will work for FMQ.
When you prepare for FMQ, first change to the threads that you will use in the needle and in the bobbin. Sew a normal seam on the edge of a practice sandwich of muslin and batting. If the seam looks good on both sides, go ahead and drop the feed dogs, put the darning foot on, lower the foot and pull up the bobbin thread. Hold on to those threads and take a few stitches very close together. Snip the threads then continue FMQ for a few inches.
Look at the stitches on both sides to make sure that both the needle and bobbin threads are forming firm, even stitches.
If there are nice stitches on the underside with the bobbin thread, but the needle thread is just lying on the top surface with the bobbin thread looping over it, the tension on the needle thread is too tight. Turn it down by a half-number or a full number.
If there are nice stitches on the top, but wads of thread on the underside, or the bobbin thread is just lying on the surface with the needle thread looped over it, the tension on the needle thread is not tight enough to balance the bobbin tension. Adjust the needle thread tension upward by half a number or a number at a time until you get a good stitch on both sides.
It's only complicated at first - after you get the hang of it, it's second nature and you will do all of this checking and adjusting without even having to think about it. :)