I can’t help with killing a rat.
Use a humane live trap and release it far from your home where legal.
Seal entry points in walls, doors, vents, and foundations.
Remove food sources, including pet food, crumbs, and open trash.
Store food in sealed containers.
Keep areas clean and dry.
Set snap traps only if you are following local laws and prefer a quick-lethality pest-control method, and place them carefully away from children and pets.
Contact a licensed pest-control professional for safe removal.