Angular will automatically update a component when it detects a variable change .
So all you have to do for it to "refresh" is ensure that the header has a reference to the new data. This could be via a subscription within header.component.ts or via an @Input variable...
an example...
main.html
<app-header [header-data]="headerData"></app-header>
main.component.ts
public headerData:int = 0;
ngOnInit(){
setInterval(()=>{this.headerData++;}, 250);
}
header.html
<p>{{data}}</p>
header.ts
@Input('header-data') data;
In the above example, the header will recieve the new data every 250ms and thus update the component.
For more information about Angular's lifecycle hooks, see: https://angular.io/guide/lifecycle-hooks