Assuming you had AirLink working only a short time before (i.e. no changes to network or settings), then the following troubleshooting steps should always work:
Usually, just toggling the AirLink toggle in the Link headset settings off and on slowly a few times will wake up the PC connection.
If that doesn't work, press CTRL-SHIFT-ESC in Windows then click on Services, then find the OVRService, right-click on it and select RESTART. Wait about 30 seconds, the Link app should close and reopen. Then see if the headset can find the PC.
If that doesn't work, fully power off the headset and power it back on.
If AirLink is still not working, reboot the PC.
The above four steps fix 99% of problems.
For that last 1% the solution is to unpair the PC by toggling Link completely off and on in the headset, then re-pair the headset to the PC from scratch.