Hi Deepika, You can apply E-Visa for Singapore, Malaysia & Vietnam ( E-Visa is cheaper that VOA).
For Malaysia apply for Entri Visa (Single entry and stay for 15 days) on www.windowmalaysia.my. Singapore Visa can be applied through MMT app or Akbartravels.
You can get VOA free in Thailand till 30th April'20.
And Cambodia VOA will cost you 30 USD.