How to calculate the delivery of a touch spell using the familiar?

Familiar Conduit text reads

Under your tutelage, your familiar has grown attuned to the hidden currents of the world and can serve as a conduit for your magic. If the next action you use is to Cast a Spell that has a range, the spell uses the familiar as its origin point.

Touch is a range, but familiars do not have the required stats to make an attack. How does one calculate the success or failure?