How much to put in my fish tank?

hi so i just buyed ammonia tablets for the fish tank that i have because there was a fish i had that one day i didnt found so every day i was lookign like at the 6 day i found it it was in bones already so i tought my tank must have a lot of ammonia anyways it says half a tablet for 10 gallons and my fish tank is 3-5 gallons how much should i put?? half of the half or how? plz i dont wantt another fish to die i had 6 now 2 :(