Per the official novelisation, Finn dragged Rose back through the breached door. The walkers ignored him and the ground troops hadn't disembarked yet.
Working quickly, Finn rigged a makeshift travois out of broken hull plating and wiring and strapped Rose to it. He didn’t have time to process what she’d said to him, before she kissed him, or to worry about how badly she might be hurt. He had to focus on getting her to a safe place. Fortunately, he remembered his survival training—or, more accurately, he’d drilled enough that it had become muscle memory, with his hands knowing what to do even while his brain stumbled and fumbled.
It occurred to him that, ironically, he had Phasma to thank for that.
There was a long crack in the door to the old rebel base now. Finn double-checked that Rose wouldn’t fall off the contraption he’d rigged, tilted the travois, and began to pull it behind him, hurrying across the salt plains toward the distant lines of the trenches.
He kept glancing at the towering walkers, fearing that at any moment one of the huge, animal-like heads would tilt their way and open fire. But the walkers simply trudged along without taking any apparent notice of them.
After a moment he realized why.
They don’t think we matter. Because they know they’ve won.
The film's junior novelisation suggests that smoke and rough ground may have also (partially) shielded them from view.
Finn stripped wire from his skimmer. The smoke had drifted past, so he
could inhale without worry. But his lips tingled strangely, probably
from the salt in the air. Or was it from Rose’s kiss? She lay on a
metal sheet he’d torn off the skimmer. He corded the wire around her
waist and her legs so she wouldn’t slip off. The leftover wire he used
to rope the skimmer’s laser barrels through the holes he’d punched
into the sides of the sheeting. He then lifted both barrel ends and
started to pull Rose on his improvised sled.
The going was tough, the ground slippery. Finn had to take a longer
route back to the mine, to avoid the thickest patches of smoke.
Whenever they were out in the open, Finn dreaded the seemingly
inevitable laser barrage. Yet for some reason, the gorilla walkers