Hi,
If you donate now, you can claim it for FY 2019-20 (ie AY 2020-21) or FY 2020-21 (AY 2021-22), its your choice.
By the by the last date to make tax deduction investments has now been extended till 31st July,2020 (for FY 2019-20).
(Apologies for my late reply!)
