Thank you Elysium, I was trying to search for AC_CONCENTRATION since I though AC meant archer, anyway, I actually wanted to modify the agi separetly, but thanks to you I found out that this code below change the agi stats.
if(sc->data[SC_CONCENTRATE] && !sc->data[SC_QUAGMIRE])
agi += (agi-sc->data[SC_CONCENTRATE]->val3)*sc->data[SC_CONCENTRATE]->val2/100;