How to make player play custom animation when sitting in seat?

-- Server Script

local Players = game:GetService("Players") -- Our player service to use the PlayerAdded & CharacterAdded events.
local SitAnimID = 507776043 -- Set to your specified animation id to replace the default sit idle animation.

Players.PlayerAdded:Connect(function(Player) -- On player added
    Player.CharacterAdded:Connect(function(Character) -- When character is added
    local Animation = Character:FindFirstChild('SitAnim', true) -- Finding the sit animation in the character
    Animation.AnimationId = ('rbxassetid://%s'):format(SitAnimID) -- Replacing animation id with yours.
    end)
end)

Hope this has helped, please learn from this and have a good day. If you have anything else you want to add on you can ask me. :)

Requested Script (Ignore)

-- Server Script

local Players = game:GetService("Players") -- Our player service to use the PlayerAdded & CharacterAdded events.
local SitIdleAnim = 507776043 -- Set to your specified animation id to replace the default sit animation.

local Seats = {
[workspace.Seat1] = 507770818;
[workspace.Seat2] = 507770677;
}
-- For each seat as the key, the value will the animation you want to play

Players.PlayerAdded:Connect(function(Player) -- On player added
    Player.CharacterAdded:Connect(function(Character) -- When character is added
    local Animation = Character:FindFirstChild('SitAnim', true) -- Finding the sit animation in the character
    local Humanoid = Character.Humanoid -- So we can use the GetPropertyChangedSignal

    Humanoid:GetPropertyChangedSignal('SeatPart'):Connect(function()
     local AnimationValue = Seats[Humanoid.SeatPart] -- if the part exists in the table as a key
     if not AnimationValue then  -- if it's not then we'll set it to our idle animation
        Animation.AnimationId = ('rbxassetid://%s'):format(SitIdleAnim) 
       else -- else if the animation does exist then it'll set to it's value that's in the table
        Animation.AnimationId = ('rbxassetid://%s'):format(AnimationValue)
      end
    end)        
   end)
end)