How to add health to a humanoid when touching a brick?

Assuming your "SafeZone" is a single part, you could do this:

ServerScript

local SafeZone = script.Parent

SafeZone.Touched:Connect(function(hit)
	if hit and hit.Parent and game:GetService("Players"):GetPlayerFromCharacter(hit.Parent) then
		hit.Parent:WaitForChild("Humanoid").Health = 100
	end
end)

You can also use the TakeDamage() function of Humanoids by using a negative number, where Line 5 would instead be

hit.Parent:WaitForChild("Humanoid"):TakeDamage(-100)