From the comments:
Sorry if I'm asking again but can I put another fuse for 20 A? instead of that resistor? is it even related to 20 A?
R15 is the current shunt. Typically it will be 0.01 Ω so that 20 A gives a 200 mV drop across it and this gives 200 mV to the LCD voltmeter module. (Actually 199.9 mV is the maximum that can be displayed.)
So no, you can't put a 20 A fuse in.
Be very aware that if you take a voltage reading having forgetton to move the leads back to V + COM after taking a current reading that you will apply a short circuit and may create an arc flash. The professional meters will have a special fuse for this circuit and replacement fuses generally cost more than a supermarket multimeter.