What should I do to get admission in DCRUST Murthal in CS branch (if my rank in JEE is not good but I belong to Haryana resident and fee waiver category)?

Admission to B.Tech at DCRUST is based on JEE Mains ranks, irrespective of your category. Since you are applying for the fee waiver category(TFW), you will get CS much higher rank as compared to the general category but it is applicable for online counselling mode only. In physical counselling, you can expect to get CS branch up to around 70k rank. Both counselling is conducted by HSTES, and you can appear for both counselling separately.