How do you update old player data in a Datastore?

I used the example Datastore code as a foundation, but I noticed that if you ever want to add or remove values from the retrieved data that it get's a little tricky. Ex.

sessionData[player] = {SBBplayerSettings = {apples= false, toOranges= false}, pearsAreOktoo = false}

When a new player joins, their data will be created to have this setup. However, if a player had joined before the update, when retrieving their data it may look more like this:

sessionData[player] = {"Experience" = 0, "Money" = 0}

I have no idea how to pull the old strings/tables and convert them to the updated format. I have however tried something like this (there is code before this that worked at figuring out which pieces are missing which is not included)

if firstTimeEntry == false then

for key,value in pairs(dataWork) do -- dataWork is the table (dataWork = {data})

    --(I moved it to the table dataWork in order for it to run smoother.)

    for keyA,valueA in pairs(value) do -- My attempt to add a key to data inside dataWork

        firstTimeEntry = true

        print("made it to the table")

        table.insert(value, firstTimeEntry)

        print("made it past")

        firstTimeEntry = true

        print(keyA,"=",valueA)

    end

end

end