angular 7 SEO change meta tags change in view html

@Injectable({
   providedIn: 'root'
})
export class SEOService { 
   constructor(private meta: Meta) {
        meta.addTag({name: 'description', content: 'Title and Meta tags examples'});
        meta.addTag({name: 'viewport', content: 'width=device-width, initial-scale=1'}); 
   }

   ------

}