Garner spent his freshman year, 2018, at Navarro College.[4] He appeared in 10 games, posting 48 tackles, five pass breakups, two interceptions and 0.5 tackles-for-loss.[5] He joined the Louisiana Ragin' Cajuns after one season at Navarro.[6] In his first season there, Garner played two games and totaled four tackles.[3] Originally a backup to begin the 2020 season, he was thrust into a starting role due to several players contracting COVID-19 and his performance there led to him remaining a starter.[3][7][8] He finished the season with 11 games played, eight as a starter, with 27 tackles, three interceptions (second on the team), seven pass breakups (second on the team), one sack and one tackle-for-loss, being named honorable mention all-conference.[3]
In 2021, Garner played in 13 games, starting 11, and earned third-team All-Sun Belt Conference honors as he compiled 31 tackles, 2.5 tackles-for-loss, eight pass breakups, a forced fumble and a sack.[3][9] He transferred to LSU in 2022.[10][11] In his only season with the team, he posted 43 tackles, 1.5 tackles-for-loss and eight pass breakups while starting all 13 games.[12] His eight pass breakups lead the team.[3] Although Garner had a remaining year of eligibility, he opted to declare for the NFL draft while accepting an invitation to the East–West Shrine Bowl.[6]