Adding announcement to multiple sitecollections

I have 3 site collections viz. HR, Marketing, Sales which are spread across multiple O365 tenants. Now I want to add a list item in an announcement list on HR Site and once it gets added I want to it be added to other sites i.e. Marketing and Sales automatically which are on separate tenants instead of manually going to the sites and adding it. Please help me in achieving this.

Any help would be greatly appreciated.