Please be advised there is no 'select all' for Enquiries to ensure that users process and complete their enquiries individually (Follow Up, add notes etc). This is also to ensure that bulk enquiries are not completed or deleted by accident as these actions cannot be undone after completing.
If you are wishing to update enquiries in bulk, you will need to click on the grey circle next to each enquiry to select it and then you can process the action from the ellipses.