Here is my current code on a plugin.

    /**
     * Field Validation.
     */
    public function payment_process() {
        if ( 'woo_bkash' !== $_POST['payment_method'] ) {
            return;
        }

        $number   = sanitize_text_field( $_POST['bKash_acc_no'] );
        $trans_id = sanitize_text_field( $_POST['bKash_trans_id'] );

        if ( '' === $number ) {
            wc_add_notice( __( 'Please enter your bKash number.', 'bangladeshi-payment-gateways' ), 'error' );
        }

        if ( '' === $trans_id ) {
            wc_add_notice( __( 'Please enter your bKash transaction ID.', 'bangladeshi-payment-gateways' ), 'error' );
        }
    }

I want to make these fileds optional by adding code on the function.php file of the child theme.