let longPressGesture:UILongPressGestureRecognizer = UILongPressGestureRecognizer(target: self, action: #selector(self.handleLongPress(longPressGesture:)))
longPressGesture.minimumPressDuration = 1.0 // 1 second press
longPressGesture.delegate = self
self.tblListView.addGestureRecognizer(longPressGesture)

@objc func handleLongPress(longPressGesture:UILongPressGestureRecognizer) {

    let p = longPressGesture.location(in: self.tblListView)
    let indexPath = self.tblListView.indexPathForRow(at: p)

    if indexPath == nil {
        print("Long press on table view, not row.")
    }
    else if (longPressGesture.state == UIGestureRecognizer.State.began) {
        print("Long press on row, at (indexPath!.row)")
        let cell = self.tblListView.cellForRow(at: indexPath!) as! GroupDetailTableViewCell
        cell.btnDeleteMember.isHidden = false
    }
}

I think you can want to hide or unhide btnDeleteMember.If so use the following code :

@objc func handleLongPress(longPressGesture:UILongPressGestureRecognizer) {

    let p = longPressGesture.location(in: self.tblListView)
    let indexPath = self.tblListView.indexPathForRow(at: p)

    if indexPath == nil {
        print("Long press on table view, not row.")
    }
    else if (longPressGesture.state == UIGestureRecognizer.State.began) {
        print("Long press on row, at (indexPath!.row)")
        let cell = self.tblListView.cellForRow(at: indexPath!) as! GroupDetailTableViewCell
        cell.btnDeleteMember.isHidden = !cell.btnDeleteMember.isHidden
    }

}

if let selectedIndexPath = self.tblListView.indexPathForSelectedRow {
    self.tblListView.deselectRowAtIndexPath(at: selectedIndexPath, animated: true)
}

//  Global variable
    var previousIndexPath : IndexPath = IndexPath()

    @objc func handleLongPress(longPressGesture:UILongPressGestureRecognizer) {

        let p = longPressGesture.location(in: self.tblListView)
        let indexPath = self.tblListView.indexPathForRow(at: p)

        if indexPath == nil {
            print("Long press on table view, not row.")
        }
        else if (longPressGesture.state == UIGestureRecognizer.State.began) {
            print("Long press on row, at (indexPath!.row)")

            let cell = self.tblListView.cellForRow(at: indexPath!) as! GroupDetailTableViewCell
            cell.btnDeleteMember.isHidden = previousIndexPath == indexPath ?
 true : false // This will make the Select and Deselect
            previousIndexPath = indexPath
          }
        }

    }

var selectedIndex:IndexPath?

else if (longPressGesture.state == UIGestureRecognizer.State.began) {
   print("Long press on row, at (indexPath!.row)")
   selectedIndex =  selectedIndex == indexPath ? nil : indexPath
   self.tableView.reloadData()
}

if let current = selectedIndex , current.row == indexPath.row {
   // selected
}
else {
   // not selected
}