How do you loop a seating animation using workspace?

I don't understand what you're saying, but I do know that this might work.

while true do
    if player.Sit == true then
        game.ReplicatedStorage.RemoteEvent.OnServerEvent:Connect(function(player)
            local anim = Instance.new("Animation")
            anim.AnimationId = "http://www.roblox.com/asset/?id=507771019"
            local loadedanimation = game.Workspace[player.Name].Humanoid:LoadAnimation(anim)
            loadedanimation.Looped = true
            loadedanimation:Play()
        end)
    end
end

Also, not being offensive or anything but please put more effort into your question.

You can use an LoadedAnimation:Stopped() event and re-set the TimePosition of the track in the time you want it to loop from. See what is the time counting of the point you want to loop from and put in the xx below:

loadedanimation:Stopped():Connect(function()
            loadedanimation.TimePosition = xx
        end)

In this case it is supposed to take the animation back to that point. But if you want to freeze the animation in its TimePosition you can change the Speed property to 0 alike - or:

loadedanimation:AdjustSpeed(0)