Hi good eveninghow can i make setting for generating automatic serial number for document like bill, expense, cheque, Journal Voucher etc?

I have some information regarding generating an automatic serial number for your transactions, madogar555. 

If the serial number you're referring to is the reference or bill number in your vendor or supplier transaction, please know that generating an automatic serial number is currently unavailable. This feature is exclusive to sales forms such as invoices. Thus, you'll need to manually enter the serial numbers in the reference or bill number field.

On the other hand, you may consider enabling the feature in the steps below to alert you if the number you're entering has already been used. This way, we can prevent duplicate numbers when entering them manually.

Here's how:

1. Go to the Gear icon located at the upper right corner and choose Account and settings. 
2. Click the Advanced tab from the left menu. 
3. Choose the Other preferences tab, then enable the Warn me if duplicate cheque number is used, Warn me when I enter a bill number that’s already been used for that supplier, and Warn me if duplicate journal number is used option.  
4. Once done, click Save, then select Done to exit the Account and settings window. 

Furthermore, you can customize reports in QuickBooks Online to get the most out of your financial reports.

Please let me know if you have further concerns regarding QBO, madogar555. We'll be around to help you.