While sitting in the Swastik Asana, recite the Gayatri Mantra. Using your knees as a frame, wrap your thread (string) around them three times, and cross the ends of the string
fold the ends toward the backside of the crossed ends and tie a simple overhand knot around the three threads
and pull tightly
pull the two ends together
and twist
tie the twisted ends with another overhand knot
finally, pull the end around and through its self in a half hitch knot