When it comes to repairing a tear in modal fabric, the best way is to use a needle and thread of matching color. If the tear is jagged, you can invisibly fuse it by using lightweight fusible interfacing.
To prevent tears from forming in your modal garments, be sure that when ironing them you avoid stretching or tugging at the fabric. Additionally, always make sure to follow any stain removal instructions closely so as not to damage its color fastness.