How can I install mod 1.7.10 on the aternos server and not on version 1.12.2?​

(Sorry my english but it is not my mother tongue) How can I install mod 1.7.10 on the aternos server and not on version 1.12.2? Me and my friends would like to play with mods in 1.7.10 but the server gives me mod for 1.12.2? How can we do? Thanks in advance for your answers !! See you later