Set the cage out, door open, in an open area with food and water, if he is recall trained, try to call him. If he doesn’t come down, use any noise he loves. If that doesn’t work, try and use his favorite treats to lure him back. If that doesn’t work, wait for him to return to his cage. The bigger the cage, the better chance he has of seeing it. But Remember, they have incredible eyesight so they will be able to spot their cage, see you. If he flies off, FOLLOW HIM but do NOT yell, do not chase, do not panic, just follow and DO NOT take your eyes off him.
Depending on where you are, he may be able survive a few days or only a few hours. If it is snowy and cold, he may not have much time. If it is windy, I would advise against recalling against the wind. Recall with the wind (as in the direction it is blowing) so he can get down easier to you and fly with the wind. If your area has many predators, that heightens his risk of getting scared and flying away because he will always see them before you. Be mindful of this.
If he is clipped, see if you can use a ladder to go into a tree to get him, but be mindful that he can still fly. A fall, depending on how the clip was done can go VERY wrong. Have him step up and then bring him to your chest and hold him there until you can get him in his cage.
This is a dangerous situation. Good luck.