Thanks for reaching out to the Community, @Hameed9233.

In QuickBooks Online, you can customize sales forms. However, for the Bill, the option to add a Discount column and calculates automatically for the net amount is unavailable. In the meantime, you can add a line item for the discount to show on the Bill.

We recognize that each company has unique needs, and I can see how the feature you're looking for would benefit and empower your business. Thus, I encourage you to submit feedback to our Product Development Team. They look through submitted feedback for future updates and use those suggestions to develop changes for the product.

You may also want to visit our QuickBooks Blog. And be the first one to know about any updates that you'll find beneficial for your business. The QuickBooks Blog is our way of letting you know the latest features released and what the product team is working on. They update the site every time new information is available. 

If there's anything else you need help with, let me know by adding a comment. I'm more than happy to assist you. Have a great day!