$re = '/^(?:[^_\n]*_){10}([^_\n]*).*$/m';
$str = 'e220juju_uk_yy_aon_aon_conversion_mystore_facebook-network_ppl_primaria_myproducta_galaxycombos_20220520
e220tyty_bo_oo_aon_aon_conversion_mystore_facebook-network_ppl_lal_myproductb_wd95m4473mw_diasdecyber_20220718
';
$subst = "\1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php