After I tried using groups, the "new tab" button that usually appears beside the tabs is gone: How do I get it back?

I clicked the Tab Groups feature and was using that for a while, but then I noticed that the button that is usally beside my open tabs (it looks like a plus symbol) is no longer there. I guess I can just use ctrl+t, but sometimes I want to use my mouse instead and the button was handy before it disappeared on me.