How to control robot car(with robotic arm) with joystick using arduino uno and bluetooth module?

The joystick sends X & Y axis data. You generally need to use code in your sketch to translate that into movement. What type of code depends on the method of movement, differential (aka tank steering) or ‘standard’ car steering, or perhaps something totally different like a walker or Mecanum wheel. Google for code examples.

If you are only interested in the “no programming” method of control in the App, then you are limited to the widgets that you can use… in the case of joysticks, you would need two of them and only use the one axis each (one for Left-Right & one for Fwd-Rev). or just use buttons.

Here is a dirt basic example of a code and button method…

Search this forum with keywords like Car, Rover, Joystick, RC, etc. for more topics about this. Do some reading and bring your questions back here (your topic) as needed.