Bonjour Jane,

The construction is il (indirect object pronoun) faut de l'aide where "de l'" is a partitive article (some).

You are correct when you interpret "il lui faut de l'aide" as he/she needs some help, but then for the same construction you interpret "il te faut de l'aide" as "must help".

I suspect that you don't realise that "te" is an indirect pronoun in this case -- the confusion may come from the fact that "te" can be direct or indirect depending on the context. 

So "il te faut de l'aide" --> you need some help.

Bonne journée

Jim