The Maruti Suzuki Ciaz has an engine oil capacity of 3.2 liters. You can follow the standard recommended schedule for most cars i.e. change the engine oil every 12 months or after every 10,000 km. According to me synthetic oils go well with the engine. I would recommend the Shell HX5 15W-40 and Shell Helix HX-7 Synthetic 5W-40 engine oils.
In my opinion if you schedule your service after 10,000 KMS you should go for synthetic oils. If your service is scheduled within 6 months of your previous service and you have failed to clock more than 8000 KMS before that service, than you should go for regular oil.