mainwp_pro_reports_custom_tokens

add_filter( 'mainwp_pro_reports_custom_tokens', 'mycustom_mainwp_pro_reports_custom_tokens', 10, 3 );
function mycustom_mainwp_pro_reports_custom_tokens( $tokensValues, $report, $website ) {
	if ( is_array( $tokensValues ) && isset( $tokensValues['[my.custom.token]'] ) ) {
		$tokensValues['[my.custom.token]'] = "Do semething here to show data in report.";
	}
	return $tokensValues;
}