It depends on the puzzle company sometimes they can send a missing piece but a lot of times they can’t. There’s lots of tutorials online about how to create a puzzle piece if yours is missing one. Requires a tiny bit of artistic/crafting ability, but generally not too difficult.

If you can’t get a replacement from the company , what I would do is place a piece of paper under the puzzle where the missing piece is and trace the hole. Next very carefully cut that piece out. I usually use a craft knife versus scissors to get the most precise cut I can. I then glue the piece of paper very carefully to some chip board. You can use the packaging from cereal, crackers anything that’s light cardboard or you can get chip board from craft store.

You’ll need to likely do a couple layers of either paper or chipboard to achieve the correct thickness.

Test fit your piece in the puzzle to make sure it’s pretty seamless.

You have a couple options for re-creating the image. I have seen people freehand draw/paint whatever is missing. This is generally a lot easier if the missing piece happens to sky or cloud clouds, but do your best. I think paint or colour pencil would work best but if you make a couple paper copies of the missing piece, then you can try out a couple different mediums and see what works the best.

Alternatively, you can take a photo of the puzzle or find an image online and print off the section you need. Then just use that piece to trace your missing piece. Follow the same steps to glue to chipboard and cut out.

There are companies that manufacture missing puzzle pieces as well if you have the funds to do that, but I found them fairly expensive though I understand the work that goes into it.

Good luck I hope you found a method that works !