You can create a lookalike audience from your Custom Audiences easily in AdEspresso from the "Asset Manager" page.
From here, you'll see a list of all of the custom audiences you have created on Facebook or AdEspresso already. After clicking the gear icon, you will find the option to delete, edit, or create a lookalike from each eligible Custom Audience you have.
When you click to make a lookalike, you'll be able to set your lookalike optimization (optimize for reach or similarity) as well as which country your lookalike will be based out of. Once this is set up, the creation will begin.
Alternatively, you can also create your Lookalike audience by selecting the green "New Asset" icon on the right of the screen, then "Create New Custom Audience" and finally choose to create a Lookalike Audience:
Keep in mind it can take some time for your lookalike audience to be fully created and ready to be used for a campaign.