How can I separate the customer by year ?

Hi admcommanding-ou,

Welcome to the QuickBooks Community. I'll be happy to share more info so you're on the right path with achieving your goals. The program is designed to help you streamline your work and I'll be glad to point you in the right direction. 

It's vital I know where in QuickBooks you're looking to separate the customer by year. In case you're referring to the reports, I encourage you to check out this helpful article that shows you how to: Customize reports. You're more than welcome to elaborate or ask other questions in the comments below. I'll be one message away in case you need anything else.