How can i datastore an leaderstats stringvalue?

As far as I am aware, you cannot save a string value. What I would suggest is to have the Rank be a IntValue also, then have a separate script that loads something like

local function onPlayerJoin(player)
        local leaderstats = Instance.new("Folder")
        leaderstats.Name = "leaderstats"
        leaderstats.Parent = player

        local Clicks = Instance.new("IntValue")
        Clicks.Name = "Clicks"
        Clicks.Value = 0
        Clicks.Parent = leaderstats

        local Prestiges = Instance.new("IntValue")
        Prestiges.Name = "Prestiges"
        Prestiges.Value = 0
        Prestiges.Parent = leaderstats

        local Gold = Instance.new("IntValue")
        Gold.Name = "Gold"
        Gold.Value = 0
        Gold.Parent = leaderstats

        local Rank = Instance.new("StringValue")
        Rank.Name = "Rank"
        Rank.Value = "Noob"
        Rank.Parent = leaderstats

            local RankSave = Instance.new("IntValue")
        RankSave.Name = "RankSave"
        RankSave.Value = 0
        RankSave.Parent = leaderstats
end

game.Players.PlayerAdded:Connect(onPlayerJoin)

then save the "RankSave" instead of the "Rank"

then I would use a script that runs in a playerGui (I like to do that because it can make and detect changes to server)

the script would read

wait (2) --gives time for data to load

onchange() --this will run the script once so that it loads up one time without detecting a value change

function onchange()
      local ranksave = script.Parent.Parent.leaderstats.RankSave
      local rank = script.Parent.Parent.leaderstats.Rank
      if ranksave.Value == 0 then
      rank.Value = "Noob"

      --Continue else if for all ranks you want to have     

      end
end
script.Parent.Parent.leaderstats.RankSave.Changed:Connect(onchange)

then as the game goes on, change the ranksave instead of the rank and this script can change the rank string value.

I hope this helps and makes sense!