how can i make a bots respawn,fight?

The only way to is when they're loaded, they get a copy of themselves so they can respawn when they die. (Replace NPC where your NPC is in the game.)

local respawnclone =  [NPC]:Clone().Parent = nil

Then, we need to tell Lua to put that clone when the NPC dies. Here's how we'll do that

while true do wait(.1)
	if [NPC].Humanoid.Health == 0 then
		wait(5)
		respawnclone.Parent = workspace
		[NPC (The one that died)]:Destroy()
	end
end
--[[You can use a "died" event btw]]--

There, that should do it. I would recommend to put the script in the NPC, so it's put with the NPC respawned.
Regards, Vivilian9