Rebirt System by standing on a circle/part/union?

Hey there i really need help for a simulator that my team is working on currently ive made a rebirth system but its gui based and not the circle stand gui pops up system currently i want a gui to pop up whenever a player is standing on that union

game.ReplicatedStorage.RebirthEvent.OnServerEvent:connect(function(player)
    if player.leaderstats.chords.Value >= 500 then -- strength needed to rebirth
        player.leaderstats.rebirths.Value = player.leaderstats.rebirths.Value +1
        player.leaderstats.chords.Value = 0
    end
end)

this is the code for the script placed on serverscriptservice there is also a rebirth event on replicatedstorage how do I make a rebirth gui pop up whenever a player stands on that circle? Please help Thank you