Excerpts are the small post summaries displayd on multi post and blog pages in WordPress. By defaults excerpts are generated from the first paragraph of post but WordPress also provides you an excerpts metabox for adding manually handcrafted excerpts. Excerpts metabox is simple text area with no visual editing options. In this tutorial we will show you how you can easily add the TinyMCE visual editing buttons (the visual editor which you use while writing any post) in your excerpts metabox.
Rich Text Excerpts is a WordPress plugin which swaps out the textarea used for excerpts with a TinyMCE editor instance. The plugin upon activation uses the wp_editor function and automatically generates a visual editor for post & page excerpts.
So what all you have to do is install and activate Rich Text Excerpts plugin and that’s it.
The plugin also provides you an options page on your admin area dashboard Settings -> Rich Text Excerpts page from there you can select which post types will use a rich text editor for excerpts, choose which Editor is used for excerpts and manage other editor options.
Same you can do with WP Edit plugin. Its admin page is divided into various tabs and from its General Tab you can activate visual editor on posts & pages excerpt area.