Angular2 Apply how to change datatable Expander icon

Question

I am using primeng datatable for my use. below is my code:

<p-dataTable [value]="alerts" [expandableRows]="true" [expandedRows]="expandedItems" #dt>
 <p-column expander="true"></p-column>
</p-dataTable>

I want to change the default icon for the string expander. Can anyone help how to change this?

thank