Finally I found the solution to this issue on documentation of wp all import
https://www.wpallimport.com/documentation/troubleshooting/encoding/
If you’re sure that your XML file is valid, it’s not using UTF-8 encoding, and WP All Import is still rejecting it, try adding this code snippet inside your child theme’s functions.php file
add_filter( 'is_xml_preprocess_enabled', 'wpai_is_xml_preprocess_enabled', 10, 1 );
function wpai_is_xml_preprocess_enabled( $is_enabled ) {
return false;
}