TP-Link T2U Plus - 5GHz band

If you have 2.4GHz wireless working but 5GHz wireless is not being detected at all, then it's most likely a configuration issue depending on the router.

So go to your router's Wireless settings for 5GHz, and set it as per following:

(1) Mode: AC Only
(2) Channel: 140
(3) Channel width: 20 MHz

Apply changes.

Note-1: Wireless Channel can be any between supported range of your wireless adapter but keep the Channel width to 20 MHz, and Mode to AC only.

Note-2: You can find out the channels supported by your wireless adapter by: iwlist chan.

Now you may need to reboot router after the above, which depends on the make/model of your router.

If it was a case of router configuration, you would now have a working 5GHz wireless.