Todoroki can heat his own water. Hell, he can make his own water. So Katsuki gets that this is a sort of asking-without-asking.

That's fine.

Yeah.
Send me your location.

He assumes wherever Toge had been staying with his cat? Either way, once he knows he's bringing a kettle. And some of the good tea leaves he recently bought.

Todoroki has been here for him through a lot and he deserves to have the favor returned. Whether Katsuki knows how to help or not, he owes it to try.