Hello @Maxi - nice to hear from you again!
In accordance with Dublin III you are only allowed to apply for asylum in one EU-member state. Keeping that in mind I'm surprised that Italy granted him asylum since they usually check back if other countries already opened a case for him. Well anyways, he has got asylum in Italy which will be the reason for BAMF to say that his application is a so called "unzulässiger Asylantrag" (inadmissible application for asylum). They will say that he does not need refuge anymore because Italy already provided it. I fear there is no chance to reopen his case in Germany.
Source (German language): https://***.nds-fluerat.org/leitfaden/4-der-bescheid-des-bundesamtes/41-unzulaessiger-asylantrag-die-dublin-ii-verordnung/