Any tips on beating pyro slimes?

What's the best way to kill the large pyro slime? I need to kill it quickly... but I don't want to level up any more of my characters. My main party is Hu tao, Barbara, Fishl, and Tighnari. I also have geo Aether I could use, and I have Xingqiu, and I have Qiqi I could use. All my other characters are level 20 or less, I don't want to level them up. But my hydro and my cryo characters I have leveled up do nothing, and I need to kill them quickly. I'm not sure if I'm doing it wrong or something though