By default, the TinyMCE WYSIWYG editor allows Paragraphs and Headers 2–6:

$_LW->CONFIG['STYLE_BLOCK_FORMATS']=['p', 'h2', 'h3', 'h4', 'h5', 'h6'];

You can use [] to append additional options to this list:

$_LW->CONFIG['STYLE_BLOCK_FORMATS'][] = 'blockquote'; // add blockquote to list

However, you can replace the array entirely to restrict access to specific options:

$_LW->CONFIG['STYLE_BLOCK_FORMATS']=['p', 'h2', 'h3']; // only allow users to select h2 and h3

Note: TinyMCE creates new <p> tags on line breaks, so it’s best to always include p as an option in any STYLE_BLOCK_FORMATS array.