Short Term Capital Gain Tax on Share trading

Dear Sir, Query No 1 - I had lost Rs 3.5 Lakh in Intraday share trading in FY 2015-2016 but I have not shown this short term capital Loss in my ITR and I left share trading from 2015 to 2020 now I have earned approx 3 Lakh Short Term Capital Gain from Oct 2020 to February 2021 ( i.e. FY 2020-21) and now my question is how can I can take benefit of Short Term Loss in 2015 in current FY Short term capital gain Tax .... From 2015 to 2020 in last 4 Financial Year I never shown Short Term Capital Loss in any of last 4 ITR so kindly confirm is it possible to revise all last 4 year to saving Tax in current Financial Year. Query no 2 I read on google no tax exemption benefit are available for Short Term Capital Gain Tax on share trading so kindly advise if any investment option are available for saving on Short Term Capital Gain Tax .