I found a way to change a Cheque number if you accidentally input it wrong.
This works for Windows 10 install (most likely works the same for other OSes maybe not in the same location though)
Navigate to the Express Accounts install files on your computer (for Windows 10 it is here🙂
C:\ProgramData\NCH Software\ExpressAccounts\Checks
Delete the number.dat file that is your check number (ex. Cheque number 333 = 333.dat)
Then in Express Accounts goto:
View Menu > Payments of Accounts Payable
Double Click on the Payment corresponding to the cheque number of the file you deleted and wanted to change.
It should show the Check No: box as empty now.
Input the Cheque number you want to use (as long as that cheque number has not been used on another payment) and click Record.
Close out then verify that the Cheque number has change by going:
View Menu > Checks (and your should see the new change in the list to the corresponding payment)
Hope this help all the people like myself that ran into this issue.
Cheers!