Do you think you can call the FCC and ask them for the info? No. You have to learn how to Query their online database.
Sorry, I can't provide lessons, I'd have to spend some time learning exactly how their system is setup before I could give advice.
What I suggest is to go to
https://wireless2.fcc.gov/UlsApp/ApplicationSearch/searchAppl.jsp - that'll take you to the FCC Universal Licensing System Search. You will find lots of Help/How-To documentation there.
But here's a hint for you, coming from someone who used to work in broadcasting... Don't search for "5G towers." It's unlikely many new towers will be erected for this purpose. Mostly, existing towers (and non-tower sites like building parapets) will have new 5G antennas affixed to them. So what you're looking for is license applications for sites. Use the Glossary in Help to find out what abbreviation(s) the FCC uses for the class(es) of radio service you're researching. Then, consider the possibility that AT&T will not necessarily be the licensee for all the sites AT&T will be using - carriers sell bandwidth to each other all the time.
I'm going to guess that you're just a plain old AT&T customer, jazzed to learn when they'll have 5G in your 'hood. If the info is sufficiently important to you, then have at it. But also consider that license applications don't necessarily tell you when those 5G cells will be going into service.
