He didn't say it. It's not true. Just another in a long list of aggie made up shit that they repeat until they believe.
https://www.barrypopik.com/index.php/new_york_city/entry/give_me_a_handful_of_texas_aggies_and_ill_win_a_war_general_george_s_patton
World War II General George S. Patton is often quoted as saying: “Give me an army of West Point graduates, and I’ll win a battle. Give me a handful of Texas Aggies, and I’ll win a war.” The quote appears on some Aggie T-shirts, but no source has been found. Most scholars believe that Patton never said it. The earliest recorded citation is from 1993.
Misattributed
Mike Province, founder and president of The Patton Society calls this an urban legend and in the Texas A&M Battalion (2 October 2006) is quoted as saying “I’ve gotten e-mails and questions regarding that quote for several years… People will use it with Texas Aggies, The Citadel, Virginia Military Institute and even Clemson. All of these schools want to be linked to Patton… Anything is possible… I honestly don’t believe he said it, because I’ve heard too many people say that he said it about their school. But if anyone out there can find proof that he said it, I’d love to hear about it and get it out there.”