From the home page screen > blue navigation bar on the left > transactions > banking > update > manage rules
On the Banking page, you can set up rules to tell QuickBooks what to do with bank items that meet particular conditions. Rules help you control, customize, and automate how you use the Banking page in QuickBooks.
Even without rules, QuickBooks makes it easier for you to accept bank transactions quickly. When QuickBooks downloads your bank transactions, it does the following:
Cleans up cryptic bank descriptions
Suggests logical categories based on bank descriptions
Remembers changes you made before, and applies those changes to similar transactions
Looks for matches among the transactions you already entered into QuickBooks
Rules go beyond the automatic processing to give you a finer level of control. They scan downloaded bank items for certain criteria you specify, and then assign particular payees, categories, classes, locations, and more to them. Rules can even help automatically split items between categories and more.
You might not need rules, but for frequently downloaded items they can save you lots of time. Here are some sample rules:
Categorize expenses at Mountain Hardware less than $50 as Landscaping
Categorize expenses at Riverview Office Supply greater than $600 as Capital Expenditure
Split income from Lakeside Law Firm as 30% Services and 70% Products
Split expenses from Hillside Communication as $40 Utilities and the remainder as Office Expenses
Rules like these can save you from having to update categories and adjust transactions one by one.
Source Quickbooks Online Help