I know this is pretty late but if I understand what you are asking, you are asking how to make it so you can get the same item multiple times and be able to have multiple of that item.
SpinnerContents in ReplicatedStorage change line 15 to false
In SpinnerServer in ServerScriptService change on line 88
--Original Code
local newStat = Instance.new("ObjectValue")
to
local newStat = Instance.new("NumberValue")
Right under that make a new line and put
newStat.Value = 1 --how much you obtain for finding it
Line 85 change
--Original Code
leaderstats.Cash.Value = leaderstats.Cash.Value + itemTypes[winningItem.GroupIndex].Rarity.DuplicateReward
to
leaderstats.Inventory:FindFirstChild(winningItem.Name).Value =leaderstats.Inventory:FindFirstChild(winningItem.Name).Value +1 --how much you obtain for finding it
All that is left is to change the messages that show when you find a duplicate item in lines 23-24 in SpinnerContents, could make it so it just says +1 instead of +20 cash, whatever you desire it to be.