This should be done by a professional luthier. A violin bow must be rehaired professionally because it requires extensive training and specialized tools.
Inspect the bow for structural damage. If there are no problems, then disassemble the bow and clean the parts. Cut the hardwood plugs precisely for the head and frog.
Select and prepare the horse hair. The best hair is generally considered to come from horses in northern Mongolia with the ideal amount of hairs being about 150 individual strands.
Identify the minimum allowable tension as the point where the hair still has a small amount of spring and is a millimeter away from the shaft. Cut the hair so that it is at this tension when you loosen the frog as much as possible before the nut comes out of the shaft.
String the hair on the bow and inspect it to ensure the hair tightens and loosens adequately and that it is securely set in both the tip and frog.