I run a gcode it doesn’t know where to go.
I don’t what this means. A video might be helpful to explain your problem. Also did you run the crown .gcode file that I pointed you to in the other topic? If so, did it work or not?
And the second issue is how to specify the working area for this machine
The working area is only useful in homing the machine. In the V1 maintained firmware for the LowRider, it is set to 300 x 300 and therefore you need to have the router within 300mm x and y to get the machine to home correctly. There is no other impact for this value unless at some future date you enable softstops. Solving this problem will require you to install development tools and learn how to build the firmware. Since there is a workaround (drag the router closer to the home position), I suggest you get any other problems solved first and have some fun with your machine and solve the table size problem another day.
Note that when you run a g-code file, the coordinates are relative to an origin point. Unless you reset it, that origin will be where the router was positioned when the control board was turned on and the steppers were engaged. The crown file I referenced in the other topic has g-code that reset the origin to where the router is when you run the g-code file. That is one reason I want you to run that file and give us feedback on how it worked.