How to receive data with parameter from Angular service

How to receive data from the service with parameters. I have 2 components and service. From one component I must to receive the data in the other component via the service. Look me code header.component.html

<li><a routerLink="contact-us">
<select (change)="onChange($event.target.value)">
<option>CONTACT US</option>
<option *ngFor="let coun of countriesShow">{{ coun }} </option>
</select>
</a>
</li>


header.component.ts

onChange(data: string){
this.countrySelect = this.ctry.onChange(data);
return this.countrySelect;
}


selectedcountry.service.ts

public countrySelect: any;

onChange(selectedCountry: string) {
this.countrySelect = selectedCountry;
return this.countrySelect;
}

getCountry(){
return this.countrySelect;
}


contact-form.component.ts (this component must to recieve data from header and service)

public countrySelect: any;
constructor(private country: SelectedcountryService) { }


ngOnInit() {
this.countrySelect = this.country.getCountry();
console.log(this.countrySelect) // undefined
}

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