Visit the following link to get full information about this year's and past year's cutoffs of IIST.
For admission in IIST, Kerala you score in GATE must be above 450. For machine learning and computing it must be 550+ whereas for aerodynamics, thermo propulsion, structure and design score must be above 530+. For other course it can be 450+ according to GaTE 2018 cutoff.
For safe side, try to achieve atleast 565 marks for popular streams.
GATE 2020 College & PSUs Predictor
Know your college admission chances for IITs/NITs & PSUs based on your Rank/Score
The GATE cutoffs are different for different colleges and categories.Please mention both of them so that i can help you as soon as posssible.