Increase product variation limit in woocommerce

This is what the apply_filters() call is for. It’s a hook that lets you modify the value.

In this case you want to use add_filter() with the woocommerce_rest_batch_items_limit hook name as the first argument, and then a callback function that returns a modified value:

function wpse_304237_rest_batch_items_limit( $limit ) {
    $limit = 200;

    return $limit;
}
add_filter( 'woocommerce_rest_batch_items_limit', 'wpse_304237_rest_batch_items_limit' );

Hooks are the main way themes and plugins integrate with WordPress and eachother, so if you want to start doing custom development on WordPress or WooCommerce I’d make learning them a priority.