The WordPress plugin editor is a text editor that allows advanced users to edit WordPress plugins. You can access it under the Plugins | Editor menu in the Administration Area.

The drop-down menu at the top right of the editor allows you to select the plugin to change. A list of links to the plugin’s component files appears below it. Click one of the links to choose the file you want to edit.

However, bear in mind that your changes will disappear when the original plugin author pushes an update. It’s important to accept these updates for security reasons. The plugin editor is mainly intended for use by plugin and theme authors.