Pert, for the step that delete all the files in the Arduino15 file except the preferences right?? is it correct ?? Like this... i send the photo that i try to use the solution that you gave last few days ago.
One more thing is the for the last two steps, restart the Adruino IDE ( this step i already go through it) and for the verification of board , is it just connect the arduino to pc and without go to Tools > Boards Manager.Right?? so the Arduino IDE of PC will able to verify the Arduino Uno (made in China) by itself and to make it successfully t verify and upload to Arduino Board ?