Go to Admin Menu > Configuration > Content Authoring > Text Formats and Editors.
Locate the text format you wish to apply the button to, in our example it's the Rich Text format.
Click the respective Configure button.
Once inside the configuration screen, you'll see the toolbar.
Click the Show Group Names link. This will allow you to create a toolbar group that you can put your new media button in.
In the expanded toolbar, click the Add Group button.
A dialog box will appear.
Give the Button Group a name. In our example, we call it Media.
Click the Apply button.
A blank space will appear on the toolbar with the button group name above it.
Grab your Media button and drag it into the blank space.
Click the Save Configuration button.
Now it's time to test the toolbar out.
Add a content type that uses the text editor you've configured by going to Admin Menu > Content > Add Content > Your Content Type.
Locate your media button and click it.
The Library tab makes use of media that has already been uploaded into your Media Library.
The Upload Image(s) tab provides a DropzoneJS field that you can drag and drop single or multiple image files into.
The Upload Document(s) tab provides a DropzoneJS field that you can drag and drop single or multiple document files into.
The Add Video Embed tab provides video embed field that you can paste third-party YouTube links into.