I put I got 2400 on my stimulus but I only got 1700 how do I change it? I've already submitted my taxes but they haven't expected them.

Once you have officially e-filed, even if the IRS hasn't accepted there is NO way to change it unfortunately. You have to wait for your return to be accepted, and would highly recommend waiting until after you receive your payment, to then file an amended return to claim the rest of the funds.

The IRS knows how much stimulus money they sent you, so it is possible that they will correct your tax return and refund the proper amount.