can I get all three starters by using Pokemon bank and restart the game? Will Iose all the Pokemon?
You can do so by pressing up + B( button) + x( button) at the title screen.Doing so,it will ask you whether you want to delete your save,select yes and your game will reset.
Source:my brain and this
Just in case if you dint understand,you can see a video by clicking here.
Doge already told you how to restart, so look at that. Yes, you can get all 3 starters. Every Pokemon not put into the poke bank will be deleted, and you need a Pokemon in the game at all times, so catch another Pokemon so you can transfer starters.