There is a cigarette lighter socket under the 12Volt output cover. Car Power Output (x1):
108.8W, 13.6V DC, 8A max.
You can make a suitable cable, but I wouldn't recommend it, as the Ecoflow has no charging electronics. The Ecoflow's fuse will probably blow before the car battery is properly charged. The Ecoflow is definitely not suitable for this.
But of course you can use a charger like this with the Ecoflow:
AEG LT 10.0 (12V, 24V, 10 A)