Here’s a link to a video that shows how to remove the palmrest assembly (which includes the keyboard) from a Toshiba Chromebook 2 CB35-B3330.
I realize that this is not exactly the same model number as your laptop but according to this website the keyboard is compatible with both the B3330 and the B3340 so perhaps the replacement procedure is the same.
This supplier was to show the keyboard compatibility between the two models and also to give you an idea of the cost of the part. There may be other suppliers online that suit you better. Just search for Toshiba Chromebook 2 CB35-B3340 keyboard to get results for suppliers.
Hopefully this is of some help.