Arduino Car

I have bought an arduino car and I have followed all the instructions on youtube Gbargin/Elegoo Robot Car Kit for Arduino assembly - YouTube but still does not work. The only different thing that I did is that I have inserted a 9v battery with the arduino shield but when I have taken the measuring voltage with a volt meter, the battery was 6.8 volts and the arduino batteries should be 2 x 3.7 volts which in my country we do not have. Can be this the problem? How do I check if arduino uno, motor and shield board functions well?
I have tried the blink program and it works well. I have tested all motors and all work fine. When I switch it on the servo goes on the left direction and remains there. The car also does not move at all.

If you are going to ask questions pertaining to a device called the Arduino Car, (which is not listed on the arduino products page, you need to post a link to the vendor where you got it. We have no idea what you are talking about . At this point , there could be 10000 arduino cars , all different, all made by different companies , sold around the world.
Please post a link to the product you purchased.

Short answer: the car will NOT work with a 9V battery.

If it was designed to run on the 3.7V Lipo batteries not sold in your country then you have 2 options:

Option 1: Use a AA battery pack of 4 to 6 batteries in series (6 to 9V)
Option 2: Try to buy a 1350 mAh 2S lipo battery on ebay on online and have it shipped to your country

Long Answer:
You should research things before buying them. The 3.7V batteries are called Lipo batteries. They come in different sizes and combinations of cells. The closest to 9V is a 2S (don't know what mAh rating the car batteries are supposed to be. Most Lipo batteries these days are at least 35C, meaning the DISCHARGE rate can be up to 35 times the 1C charge rate. The 1C charge rate is the rating of the battery. So if the battery says 1350 mAh on it and 35C, then it can be discharged at 35 x 1350mAh = 47.25 A.
1.35A h (1350 mAh) , if discharged at the rate of 47.25A , would last 1.35A/47 = 0.028 hours (1.72 minutes (103 seconds) Likewise a 1350 mAh rated Lipo battery (1.35A h) if discharged at 2C , instead of 35C would last 1.35 Ah/2 = 0.675 hours (40.5 minutes), and so forth.
The 9V PP3 rectangular smoke alarm battery you used is rated for 350 mAh.
Lipo powered devices are typically designed to last about 10 minutes on a single charge , although this is not a rule and the "RUN TIME" of a Lipo powered device can be anything. The point is that if the arduino car (whatever that thing is, which , at the moment, I have not the faintest idea) was designed to operate for 10 minutes on a single charge, it is possible it is designed to use 1350 mAh 2S batteries, which would have a fully charged voltage of 8.4 volts. 1.35 Ah/8A = 10.25 minutes. The 9V battery, rated for 350 mAh (0.35 Ah) would not be able to source (supply ) enough current to power the motors due to internal resistance of the battery. The calculations that apply to Lipo battery do not apply to high internal resistance batteries such as a PP3 9V smoke alarm battery. The instant you turn on the car, the battery would drain immediately (which it obviously did).

If the car was designed to run on the 3.7V Lipo batteries not sold in your country then you have 2 options:

Option 1: Use a AA battery pack of 4 to 6 batteries in series (6 to 9V)
Option 2: Try to buy a 1350 mAh 2S lipo battery on ebay on online and have it shipped to your country

The video here

shows what looks like 4 AA batteries in series (6V)
That appears to work. You could stack THREE 2-battery packs on top of each other (6*1.5v= 9v) and wire them in series for 9V.

The batteries you need are THESE

GOOGLE "18650 3.7V LIPO BATTERY , ebay"