I would like my Score Manager to update

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4

Actually, I do not have time to write custom solutions but here this is how you could write your code in a very simple straight-forward way:

if (score >= 1000)
{
    float value = score / 1000;
    scoreText.text = value.ToString() + " Gigabytes";
}
else
{
    scoreText.text = score.ToString() + " Megabytes";
}

And if you want to add more rules, you simply add more else-ifs.