The obvious way is to butterfly away Frankish hegemony in Belgica and their previous regional integration as laeti and federates.
Basically, the simpler would be to prevent or rig enough the western germanic leagues of various tribes that gave birth to Frankish peoples : a greater intervention or domination of Rome in the region could do it relativly easily.
Eventually, another league dominated by other tribes would appear on the other side of the border (either Rhine/Weser Germans entierly, or North Sea Germans, if not both) which would give birth to a more or less similar people which would be called differently, let's say "Liges" or "Ligians" for the sake of convenience.
With the fall of WRE, if it's still happens (which is not granted, and would give another easy way to butterfly away France), the fight between post-Imperial entities may give them or other peoples the domination of Northern Gaul which would take their name.
Any PoD after the IVth century, while still able to prevent a Frankish hegemony in Gaul, would probably still see a region of Gaul called Francia, would it be only in Belgica. Now, how long it would last depends of butterflies.
If you meant less France as issued from Francia, and more France as one entity in Western Europe roughly corresponding to IOTL borders, that's going to be more tricky.
Prevent the Roman conquest of Gaul, that structurated durably the region into 2/3 regions (roughly, South, North and East) may be a good start, as it would keep alive the pre-Roman structures that were more transversal.
Indeed, even after the fall of WRE, Romano-Barbarians hegemonies were disposed along late Roman structures, essentially the North/South disposition : eventually, it formed the establishment of religional domination over these lines quite hard to go against.
Meaning that even with Franks defeated and strike-trought of History, you'd find some other power (Romano-Barbarian or Gallo-Roman, while the distinction wasn't nearly as clear and blunt : both societies mixed a lot in Late Empire) to fill roughly the same regions.
Now, if you wanted a reduced France, it gets easier with a more recent PoD. Basically, "France" designated a more reduced country inside the Frankish then French kingdom : more or less the region corresponding to Neustria and Austrasia.
Preventing the Visigothic defeat and collapse, or having Carolingia being cross-divided instead or longitudinal divide, or preventing Capetian takeover of southern Gaul at the profit of someone else...