Are you looking to add Global Button Settings Support for the WooCommerce Buttons? Now with the Astra Theme version 2.5.0, will be resolved –
For New Users:
On your fresh or new installations, compatibility of Global Button Settings will be provided for the WooCommerce Buttons by default.
For Existing Users:
You can use the following filter in the child theme』s functions.php to provide Global Button』s Support for the WooCommerce buttons.
add_filter( 'astra_global_btn_woo_comp' , '__return_true' );
Note
Refer this doc on How to Add Custom PHP Code?