SN65HVD233: How I use the loopback for it ?

The datasheet says:

10.3.1 Diagnostic Loopback (SN65HVD233)

The diagnostic loopback or internal loopback function of the SN65HVD233 is enabled with a high-level input on pin 5, LBK. This mode disables the driver output while keeping the bus pins biased to the recessive state. This mode also redirects the D data input (transmit data) through logic to the received data output pin), thus creating an internal loopback of the transmit to receive data path. This mimics the loopback that occurs normally with a CAN transceiver because the receiver loops back the driven output to the R (receive data) pin. This mode allows the host protocol controller to input and read back a bit sequence or CAN messages to perform diagnostic routines without disturbing the CAN bus.

If the LBK pin is not used it may be tied to ground (GND). However, it is pulled low internally (defaults to a low-level input) and may be left open if not in use.