Ionic selectable option

Hello , I am using Ionic selectable tag to have a drop down to select the data I have .
I am able to use multiple selections, searching , clearing all , but I am not able to select All or deselect all at once . How can I use it. Help me add the the selectall/deselect (toggle) button in the dropdown.
This is the code:
*ngIf=“userListLoading == false”
placeholder=“Select the user”