Is d3s hybridization is possible I know yes but please explain how?

This is a formally Mn(VII) compoud and hence there are no 3d electrons. The four O2− ions are considered to be donating two electrons each to the Mn Atomic Orbitals. Now most chemists didn`t realize that tetrahedral "hybridization" can be achieved by using the 4s,3dxy,3dyz, and 3dxz AOs. Since in Mn(VII) the 3d AOs are lower in energy than the 4s and 4p AOs the "hybridization" is best considered as d^3s. I have put "hybridization" in quotes because it is not used in advanced chemistry (it is an artifact!) but it is correct in saying that the bonding MOs contain mostly 4s,3dxy,3dyz, 3dxz character but they`ll also probably mix some 4p character in there for good measure!