When you need to requeen a hive, you are introducing a complete stranger to a closed society. She is not going to be immediately accepted. There are several things you can do to increase the likelihood of successful acceptance.
First, transportation: The queen lives in a dark, high-humidity, 94 degree temperature environment. You need to duplicate that environment as well as possible. She is normally transported with three or four of her old workers. They have candy available for food. Try to keep her out of direct sunlight, warm but not hot (comfortable for you), and humid, A damp towel in a box with a loose lid can be a great way to transport.
Queenless hive is required. Are you sure there is no queen? How do you know? A queen in the hive will cause the hive to reject and kill the queen in the cage. To test and verify, if you have a queen-right hive, take a frame of eggs and young brood and place it in the middle of the suspected queenless hive. Check back in three days. If truly queenless, they should have started making queen cells. If so, you can destroy the started queen cells and introduce your new queen
Introduction: First, the simplest is to remove the cover (often cork), if existent, from the candy plug end of the cage. Suspend this cage with the candy end up between two frames of brood and the screen open to the bees. The candy end is placed up so that a dying worker in the cage does not block the exit hole. The screen is open to the bees outside the cage so that they can pick up her scent and get to accept her.
Acceptance is improved by removing the workers from the queen before introduction. This helps in a couple ways. First, the workers are more likely to be rejected than the queen. Second, the loss of her old workers forces the queen to beg food from the bees outside the cage, speeding up the scent dispersal and thus acceptance.
Time is needed. Acceptance is improved if the queen id kept caged longer so the candy plug can be kept capped for a week before exposing the candy plug.
Acceptance is greatly improved if the bees in the hive are all young. This can be created by pulling frames of open brood from a queen-right hive, shaking all of the bees off of them and place them in another hive body above a queen excluder over the brood box. Nurse bees will go through the excluder and cover the brood. After two hours, these frames of brood can be moved to a nuc or the whole brood box can be moved to another hive stand. After another couple hours, the field bees will have left his new hive/nuc and returned to the old hive. This leaves a colony comprised of just young bees that will more readily accept a new queen. Once the queen is accepted, you can then combine this hive with the one to be requeened and her new workers will protect her against attack by the hive bees.
Combining two hives can be performed by covering the hive to be requeened with a layer of newspaper, cut a couple slits in the paper between a couple frames and then set the brood boxes of the hive with the new queen on top, Provide a top entrance for the top hive and leave them for a week to complete the merger.