Hello,
Here you can find our changelog https://themeforest.net/item/woopress-responsive-ecommerce-wordpress-theme/9751050?s_rank=4 , thankyou.php file was removed in 6.0 version of the WooPress, so you can delete this file.
quantity-input.php will be fixed in the next theme update that will be released soon.
Please do not update the WooCommerce if you are not sure that it is fully compatible with the theme version, next time. Information about the compatibility you can find in the changelog.
Regards