We can convert Mn²⁺ into Mn⁷⁺ by reacting with: 

Strong oxidising agents such as PbO₂ or sodium bismuthate (NaBiO₃) oxidise ${\mathrm{Mn}}^{2+}\text{ to }{\mathrm{MnO}}_4^{-}\text{or }{\mathrm{Mn}}^{7+}$

$2{\mathrm{Mn}}^{2+}+5{\mathrm{PbO}}_2+4{\mathrm{H}}^{+}\to 2{\mathrm{MnO}}_4^{-}+5{\mathrm{Pb}}^{2+}+2{\mathrm{H}}_2\mathrm{O}$