I forget exactly how to do it for the Default UI, but definitely, the first step is to press Ctrl+P on your keyboard to pull up foobar2000's preferences.
From there, if you're using Columns UI, you'd go to "Display->Columns UI->other tab->Reset toolbars"
If you're using the Default UI, I'm pretty sure there's a "reset toolbars" button somewhere in "Display->Default UI", but again, I really can't remember.