Here is the solution for you.
1. click "Settings" in game and then click "Controls". After that, select the third control method and then click "Customize".
2. Interchange the button for firing at the left side with the one at the right side. Press the F12 key on your computer keyboard to open the Keyboard maping and then move the left firing button to the right position. At last, click "Save".
You can normally change your view when you are throwing the grenade after doing these things.