Need details on how to submit malware sample

Dear Sir/Mdm,

My company do security audit for my customer wordpress site, and during our inspection, we found this suspicious file which then we check at virustotal seems to confirmed it was indeed a malware. But it seems your plugin didnt detect it as malware, so as per above title, how can i submit the sample for your analysis. Its a whole body of malware, so its not injected into legitimate app code.