How to change the default settings for toolbars in Excel of 2013?

Hi and welcome to the forum

Could you be a bit more specific? Do you want to add items to the quick access toolbar? Or change things on the ribbon? Both can be done from File > Options.

Or are you wanting to add custom items to the ribbon, pop-ups, etc - which is a lot more complicated

I also noticed you are asking a question about 2013, but your profile says you are using 2016