Have you cleansed the item, say, through incense smoke or something similar?
After it’s cleansed, you need to do something to consecrate the item to Dantalion. Yes, it’s his sigil, but by themselves, they’re just lines. Since you didn’t create the item yourself (not a dig), you’ll want to do some sort of personal ritual to imbue it with the intent of it being for Dantalion and to act as a gate for you.
The ritual itself can be as complicated or simple as you like. You could use the petition ritual in the tutorials, if you want something to go on. Instead of writing the petition on paper, you’d ask Dantalion to help the amulet become a representation and gateway.
I’m sure others could say more. It’s not an area that I work in often. I noticed this last night before bed and wanted to reply, since no one else has yet.