Please help me how to STOP [WLAN access rejected: incorrect security] from MAC address XR300

You have posted your message in the section of this community given over to Nighthawk WiFi Routers. (This is easily done, given Netgear's complicated community structure.)

Many questions apply to different types of device, so there may be useful responses here. However, the XR300 is a differenr beast with its own dumaOS operating system, so you might get more help, and find earlier questions and answers specific to your device, in the appropriate section for your hardware. That's probably here:

Nighthawk Pro Gaming Routers - NETGEAR Communities

I will ask the Netgear moderator to move your message.

In the meantime you could visit the support pages:

Support | NETGEAR

Feed in your model number and check the documentation for your hardware.

You may have done this already. I can't tell from your message.

I mention it because Netgear stopped supplying printed manuals and CD versions some years ago and people sometimes miss the downloads.