Look here from Ross Tech

Am sure it will be inside the front door

looks like this

I would be checking wiring at door loom first 

Plenty of posts about fixing on here

Okay thank you so much Sir.

As already suggested I would 1st check the door wiring inside the rubber gaiter where the loom goes into the door. You're likely to find several damaged wires in there. The wire insulation becomes hard and brittle and eventually the wire breaks. It's a common fault right across the Skoda, VW, Seat range. 

 

I think the air bag sensor is the one with the yellow plug bottom left of the door. You will need diagnostic equipment to clear the error code to turn the air bag light off.

Thank you so much sir

Hi I have checked the wiring also okay and that sensor wire is good condition continuity is came. But problem not solving. Then What is the next step I don't know. How can I checked the sensor.

So probably the sensor is faulty. Have you tried googling to find a way to test side impact sensors.

Okay thank you so much

I have had this go on mine (airbag light on). As someone has said above, the wiring in the door panel becomes brittle and breaks with age, especially in hot/cold climates’. We get -28C to +28C and it plays havoc on door looms. (within the door and at the point where it goes across the door to the front wing panel). Mine is a 2010 car and loom broke bang on a decade. Happened on my wife's Lupo back in the day too.

 

Its easy to fix (door disassembly aside) as it is a plug in/plug out bit of the loom. Good luck with it.

What's the part no of that sensor.

 

How much cost of the sensor