reset paginator first page angular material

You need to use a ViewChild decorator to select the paginator and then set the pageIndex property of the paginator.

@ViewChild() paginator: MatPaginator;
...
this.paginator.pageIndex = 0;

Edit: As suggested by the other answers, if you would like to reset the paginator to the first page, it would be better to use this.paginator.firstPage()

<mat-paginator #paginator [length]="length"
               [pageSize]="pageSize"
               [pageSizeOptions]="pageSizeOptions"
               (page)="pageEvent = paginationClicked($event)">
</mat-paginator>
@ViewChild('paginator') paginator: MatPaginator;
this.paginator.firstPage();

Create a referecne for material angular paginator along with data source

dataSource: MatTableDataSource<any>;
@ViewChild(MatPaginator) paginator: MatPaginator;

You want to reset the paginator using the following code

this.dataSource.paginator = this.paginator;

You can also reset by calling the first page method of the paginator

this.paginator.firstPage();