I’ve already filed and my return hasn’t been accepted yet from IRS. I want to change my back account for direct deposit.

Once a tax return has been filed it cannot be changed, canceled or retrieved.  The bank information for direct deposit cannot be changed once the tax return has been filed.

If the IRS accepts the tax return and the bank information is not correct, then the bank will reject the deposit and return the tax refund back to the IRS.  The IRS will then mail a refund check to the address on the tax return.

Sorry it's too late to change it after you filed.  Unless your efile rejects , then you can fix it and resend it.  Do not amend to change the bank account.  If you need to amend for something else you should wait until the original return is Accepted and the IRS is done processing it and you get the first refund or pay the tax due.  

If the bank rejects your refund deposit they will send it back to the IRS and the IRS will mail you a check.