Once they have gone.
Put up a screen, quickly as if this is a good season in your local area that might have another brood.
The birds born there will come back next year to nest in the same or nearby place.
Save the old nesting material, pop up your new birdhouse near by & put the old nesting material in there.
Use plastic gloves when removing the old material and again when replacing it,
The nest box need to make the bird feel secure, not pretty and what most do is make the entry space too big or the roost in front of the nesting space too big.
Good luck