If I want to get below 1000 rank in kcet exam then what should be my score??

The merit list of KCET is decided on the basis of the exam score as well as the board percentage of the candidate. Hence in order to achieve a rank below 1000 you need to perform in both. There's no particular marks I could tell as the cutoff changes every year because it depends on various dynamic factors like number of students appearing in the exam, availability of seats and difficulty level of the exam.
But in general you need to score more than 170 in the kcet exam if you have a board percentage of 95% this might fetch you a rank around 1k.
Hope it helps.
Thank you.