WooCommerce related products load random posts per page

You need to change the value of $orderby. Maybe the current value of $orderby is rand

'orderby'              => $orderby,

Now you need to change the value of **orderby => ” ** according to your need. for example

'orderby' => 'title'
'orderby' => 'menu_order title'
'orderby' => 'comment_count'
'orderby'   => 'meta_value_num'
'orderby'   => 'title menu_order'

Order & Orderby Parameters
orderby (string | array) – Sort retrieved posts by parameter. Defaults to ‘date (post_date)’. One or more options can be passed.

1. ‘rand’ – Random order. You can also use ‘RAND(x)’ where ‘x’ is an integer seed value. Note an “order” parameter needs to be present for “orderby” rand to work.
2. ‘ID’ – Order by post id. Note the capitalization.
3. ‘author’ – Order by author. (‘post_author’ is also accepted.)
4. ‘title’ – Order by title. (‘post_title’ is also accepted.)
5. ‘name’ – Order by post name (post slug). (‘post_name’ is also accepted.)

More details
https://codex.wordpress.org/Class_Reference/WP_Query