MacBook Air has stopped accessing internet wirelessly via ATT Pace Wi-Fi Modem 5268AC

Modem has been rebooted several times over past few weeks as have been dealing with this issue. Since the iMac sitting in the same room with the Air is having no difficulty connecting wirelessly I can't see how a reboot would have an impact on the Air. I rebooted the computer as well. While at the Apple Store Genius Bar the tech removed the DNS Server information and replaced it automatically with a series unique to Apple. But when we got the Air back home and powered it up, those DNS server numbers were missing. So, I tried using one of the two DNS server listings on the iMac (192.168.1.254) on the Air. No impact - won't connect to internet wirelessly through the wi-fi modem. I then tried adding a second DNS server number also on the iMac to the DNS server on the Air (2600:1700:c1a0:31c0::1) and it had no impact either - no ability to connect to the internet wirelessly. I'm stuck.

I resolved issue by deciding that since the iMac and Modem were "talking" to each other wirelessly without difficulty, whereas the Air and Modem were not, I would try to tweaking the "language" the instruments were using. And it worked.

On the iMac, I changed the AT&T Wi-Fi Modem Network Name and Password to another set and determined that the iMac connected wirelessly through the modem to the internet without difficulty. I then changed the iMac back to the AT&T originally assigned Name and Password and the iMac continued to connect wirelessly through the modem to the internet. Having confirmed this functioning, I entered the AT&T assigned Name and Password used on the iMac onto the Air and the Air immediately connected wirelessly to internet. No hesitation or difficulty. After two days use with the Air being on, in sleep, being shut down and being started up a number of times, the Air continues to connect and hold the connection perfectly. Therefore, issue solved. Of course, I then had to enter the AT&T assigned Name and Password on all other devices (iPhones, iPad, and television receiver) so they would connect wirelessly to the internet and they all do, perfectly.

This is a solution that you may wish to make note of for future recommendation to others.

Although your specific recommendation did not resolve the issue, I thank you for providing a thought and recommending further troubleshooting.