If I recently discovered that the account number for direct deposit was entered off by 1 number how do I go about correcting this? Or what would be the next step?

If you've already filed your return, you cannot change the account number. 

The IRS will try to deposit the refund several times.  Your bank will return the funds to the IRS. The IRS will then issue you a paper check, resulting in a tax refund delay of up to 10 weeks [according to the IRS].