Best answer by Dinh
Someone mentioned that if you saw that screen you were in “download mode”. if it was a mistake, try to push volume up + home button + power button until you see the Samsung logo then release
https://www.ifixit.com/Answers/View/124720/Doesn't+turn+on+and+says+to+download+custom+OS.#answer173240
If the phone doesn't have the home button you could try this video https://youtu.be/VNDwatZ-ooo