You cant convert the manual transmission to automatic transmission, it has to be done at the factory when the car is built. There was an automatic variant of the Santro few years back but now its no longer available.
You can easily book a Hyundai Santro Xing from there by approaching to the authorized Hyundai dealer through phone or email. All you need to do is, talk to the dealer and arrange the booking amount and you can get the delivery of the vehicle upon your arrival in the country. To get details of the authorized Hyundai dealers in India, Kindly visit the below link: -
There might be two problems regarding this issue in Hyundai Santro Xing. Either there are some dirt particles present in the throttle body of the vehicle or there might be some issue with the sensors. Kindly take your vehicle to the authorized Hyundai service center and get it checked there by a professional mechanic.