Take this beautiful shelled wonder and put it away from the swamp and dangerous dinos. After that start shooting it with darts in the head until knocked out. When it is knocked you will have to feed it sweet veggie cakes until tamed. After that you will enjoy your cement pooping machine😎
For general info about domesticating a wild creature see Taming.
Since damage is significantly reduced by the shell, it is best to hit it on the soft, fleshy parts instead. If it takes enough damage, it will retreat into its shell, making it very easy to kill it before the torpor from tranquillizers can knock it out. Be mindful of how bloody the Achatina gets, and use Shocking Tranquilizer Darts or normal Tranquilizer Darts to minimize this risk.