Why all those complicate answers about simple question.
If you in advance have options which have to be selected, you can do it simply this way :
This code is good :
HTML
<select multiple [(ngModel)]="myModelProperty">
<option *ngFor="#item of myOptions" [value]="item.value">{{item.name}}</option>
</select>
ANGULAR
myModelProperty: any;
myModelProperty = ['YOUR_VALUE', 'YOUR_VALUE'];
or if you have string, you can parse it
myModelProperty: any;
myModelProperty = string.split(',');
So, all you have to done is that [(ngModel)] from select tag, have to be initialized in angular part with some array of values which correspond to [value] from option tag
This will automatically select one or more options depends on values from array.
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