How would i tween a velocity but keep it in the direction of player

[JustChillForIt (spiderman)]

so i have a bodyvelocity that constantly moves the player in the direction theyre looking

but i dont know how to also tween it or something of the sort to make it slowly decrease in speed
is there a way to tween a variable or the speed of the velocity while keeping the direction ?

[CZXPEK (czo)]

local Decrease = 0.1
local VelSpeed = 2.5

local Players = game:GetService("Players")

Players.PlayerAdded:Connect(function(Player)
	Player.CharacterAdded:Connect(function(Char)
		task.wait(5)
		
		local Root:Part = Char:WaitForChild("HumanoidRootPart")
		local X,Z = 1, 1
		
		local Vel = Instance.new("BodyVelocity")
		Vel.MaxForce = Vector3.new(1e5, 1e5, 1e5)
		Vel.Parent = Root 
		Vel.P = 1e4
		
		Player.Chatted:Connect(function(Str)
			X = tonumber(Str)
			Z = tonumber(Str)
		end)
		
		task.spawn(function()
			while true and task.wait() do 
				local Dir = Root.CFrame.LookVector*VelSpeed
				
				X = math.max(X-Decrease, 1)
				Z = math.max(Z-Decrease, 1)
				
				Vel.Velocity = Vector3.new(Dir.X*X, Dir.Y, Dir.Z*Z)
			end
		end)
	end)
end)