Hi Krittaya-
If you have the BoldGrid Inspirations plugin active, a couple of menu items have been re-named. Specifically, Appearance is called Customize. You can switch back to the default WordPress menus by going to Settings > BoldGrid Inspirations and disabling the option to Use BoldGrid admin menu system.
That being said, the right place to change which page is your front page is not normally under the Appearance menu. Navigate to Settings > Reading (or Settings > Blog if you’re using the BoldGrid menus). Here, you’ll find the option for Front page displays: and you can change it there.