EWS reservation can be availed by all Indian Citizens who fulfil the eligibility criteria. The eligibility rule states that a Candidate who belongs to General Category and doesn't claim reservation benefits of other Categories like OBC,SC,ST and whose annual income from all sources is less than 8 lakhs per annum can avail this reservation. So in other words, you should belong to General Category and then your family income should be less than 8 lakhs per annum. If you fulfil this criteria, though you have studied Medicine abroad and want to study your Masters here in India, you can avail this reservation