If you are using the WYSIWYG editor, the alignment should be done in the editor itself and not the media manager. In EasyBlog 3.6 below, we added the alignment but it does seem like it causes more issue because generally most WYSIWYG editors are already handling this.

Since you are using TINYMCE, go to your plugin manager, click on TINYMCE. Then, change the mode to "Extended" or Advanced"

You'll have more buttons in your editor