Field upgrade; how to use?

It's been a long time since I've played anything online, I used to game a lot when I was slightly younger, lol. But I never got into the newer zombies on the other game, until now .. mostly cause Im sick of playing multiplayer with people on PC, it's not fair 😅 lol. I even tried turning off playing with others outside Xbox and I could never find a lobby...

Anyways sorry, distracted... Lol. How do I use a field upgrade, once it's charged fully, on zombies, o Xbox? I feel like I try every button, but it doesn't work 🤣 or maybe I've hit the right one and not realized it worked.

I also actually have no idea how the bubblegum things work either. 🤣🤣🤣

I can barely play past level 24 for the most part anyways. I always have to leave, cause I have a newborn and obviously can't pause the game when she needs something 🤣 So I don't even bother with anything else.

I also only just learned how to upgrade a weapon by listening to a girl teach her friend what he needed to do the other day 😅 I was like oh that's cool. I didn't know that... Lololol and now I'm glad my weapons work better.

Sorry for the novel long post 🤣