This restricts blood circulation and the foot will swell and eventually could cause the bird to die. Remove the band. To do this you may have to cut it off. This will maybe be a two person job. Be careful, that is a tiny fragile leg.
Strings are dangerous.
Birds love to play with them. There is a possibility that the string could get tangled around a birds leg or neck and get caught on the cage, thus injuring the bird. Simply be sure the strings are two inches of shorter. Shredded burlap works great for nesting material. I cut the burlap into two inch squares and shred it.