In cut-of list for 2019 CSAB for round 1, IIIT Allahabad for homestate and Gen-EWS category OR and CR was 6553 and 7867 respectively. Does that mean a candidate with EWS 3587 has the chance to get the seat.

Dear student,

Csab special round counselling is conducted by central seat allocation board and is organised for filling the vacant seat into NITs, IIITs, gftis and IIEST.
Now in CSAB special round counselling your category wise CRL ranks is used for counselling and seat allocation .

Now, last year the cutoff ranks for iiit allhabad, information technology in csab special rounds 1 counseling for ews candidates on the basis of their crl ranks was ( under gender neutral) :-

OPENING RANK - 6553
Closing rank - 7867.

This is not the category rank. This is the the cutoff CRL RANK for ews category candidates. Which means if an ews category candidate secures an ews rank of around 850, then only the candidate can secure a crl rank of around 7800, and then the candidate will get seat in this particular branch in csab. As you have secured 3587 ews rank, then your CRL rank must be around 30000.
So, there is no chance that you can get iiit allahabad.

And also check out the following link to know more about csab special round counselling and the previous year cutoff Trends ( note that all the mentioned ranks are CRL rank not category wise ranks ) :-
https://engineering.careers360.com/articles/csab-special-round-for-nits-iiits-and-gftis

Also check out our jee mains college predictor tool to get an appropriate idea of colleges that you can get on basis of your jee mains rank :-
https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer