hey,

yes you can definitely  inlcude computer science instead of chemistry but all rest three subject remains constant, that is you need to calculate aggregate of best four subject in those best four you have to necessarily include english , physics and mathematics but its up to you whether to include chemistry or computer science.

i would suggest you to include in which you have secured maximum marks.

for more information kindly refer to the link mentioned below

https://university.careers360.com/articles/du-bsc-eligibility-criteria

all the best!