It is fairly normal for people to pull up jeans on to their hips by tugging on the loops provided for the belts in the jeans. And the tighter the jeans are the harder the pulling tends to be. There are two issues that you are likely to face due to this - ripped up fabric under the loop and a loop that hangs and cannot hold a belt any longer.

The material that you will need to repair this include the jeans, denim thread, a small piece of fabric, temporary spray adhesive and jeans gold thread to make the jeans look as good as new. The first step is to assess the size of the hole and cut some fabric that is larger than this hole. Use as much of the fabric of the jeans to fill the hole and then place the patch on to the gaping hole. Use the temporary spray adhesive to hold the patch in place. This is something that will also help the thread of the torn fabric in place. You can also use some fusibles at this stage but this does not free you up from sewing.

Thread the sewing machine with the denim thread and place the jeans with the top side on top. Use a elongated zigzag stitch. Then switch the sewing machine to a straight stitch and sew back and forth over the hole - first horizontally and then vertically.

In the end you will need to attach back the loop. For this remove the threads that were used to hold the loop originally and press the belt loop in position. Make sure that you sew just on the loop so that the area looks neat and tidy after you are done. Trim all the threads and you should be ready with your jeans.