I think the way to use an amber necklace is to have it be pretty tight around the neck so the child won’t be able to chew on it. This makes sense because there is a pretty good chance the baby would tear up their gums on the sharp pieces of amber or break the necklace. If I remember correctly the recommendation is to wrap the necklace a few times around the ankle when sleeping to avoid the chance of it getting caught on anything and strangling the child in their sleep.
I’m not discouraging you from using it, maybe it’ll work, but be sure to find out the safest way of using it.