Filtering posts by author

Hello everyone!
I need to show on a page, a grid of posts of a given author. For this, I duplicated the file config-template-builder/avia-shortcodes/blog.php into blog-author.php.

Then I tried to replicate this block of code
array( “name” => __(“Which categories should be used for the blog?”, ‘avia_framework’ ),
“desc” => __(“You can select multiple categories here. The Page will then show posts from only those categories.”, ‘avia_framework’ ),
“id” => “categories”,
“type” => “select”,
“multiple” => 6,
“required” => array(‘blog_type’, ‘equals’, ‘posts’),
“subtype” => “cat”),

and put this code:

array( “name” => __(“Which authors?”, ‘avia_framework’ ),
“desc” => __(“You can select multiple authors here. The Page will then show posts from only those authors.”, ‘avia_framework’ ),
“id” => “authors”,
“type” => “select”,
“multiple” => 6,
“required” => array(‘blog_type’, ‘equals’, ‘posts’),
“subtype” => “cat”),

the “subtype” entry should be replaced by something to query the authors… but I don’t know how to do this. Can you please help me?