It's from a Germanic tribe, the Franks, who came to dominate the country during the early middle ages.
This is only a very brief explanation. The reader is encouraged to consult https://en.wikipedia.org/wiki/History_of_France.
The Franks were a Germanic tribe. "Germanic" here does not mean "German" but represents a much broader grouping, which included Scandinavians, Anglo -Saxons (Angles --> "England"), and others who were generally north and northeast of the old Roman Empire.
Two major Frankish dynasties brought present-day France together under their rule, the Merovingians and then the Carolingians. Under Charlemagne, the greatest of the Carolingian rulers, the Franks welded together a great empire in the heart of Western Europe, covering what are now Germany and Italy along with France. After Charlemagne's death, the empire broke up and the western part, "West Francia", became what we now call France.