If we want to convert one type of flip flop into another type of flip flop, first we have to design a combinational circuit to connect it to the inputs of actual flip flop. So, the outputs of combinational circuit will be the inputs of the actual flip flop and then it will produce same output as that of the required flip flop.

A T flip flop can be converted to a D flip flop by the following table and K-map:

Formula :-

$T = \bar D.Qn + D . \bar {Qn} = D ⊕ Qn$