So, to create a lookalike audience, you must already have your customer email list. And if you don't have it, kindly generate it before you start with the steps. Let's look at how you can set up the audience from email list.
Open chrome and search the FB business manager page.
Go to all tools option, and select the audience option under advertiser.
Choose create a lookalike audience.
Fill up the source, location, and percentage of people and click on create audience option.