Hi I am trying to initilized the CheckboxSelectionModel with an itemID of ItemID="cbsmPremiumSelect"

These are the different ways I've tried it:
this._cbsmPremiumSelect = this.down('#cbsmPremiumSelect');
---------->> NULL

var gridRoot = this.down('#dgvRequest');
var select = gridRoot.down('#cbsmPremiumSelect');
------------>> NULL

From debugging I can see the itemID inside the grid dgvRequest, but I can't seem to call it.
This is the path I can see the itemID: