If your schnapps or vodka infusion is too weak-flavoured you can enhance the flavours by adding a little, little bit of sugar.
Sugar is a great flavour enhancer.
You can add the sugar directly, but because sugar is more soluble in water than in alcohol, it's usually better to make a simple sugar syrup and add it to your infusion little by little.
Never use artificial sweeteners - NEVER! You will ruin the taste.
Add the sugar syrup to your infusion. Little by little, until it suits your taste.
Leave the infusion for a couple of days to settle - in a dark place at room temperature.
Then taste it again, it might need some more sugar syrup.