I would like to know the method to calculate covalencies of transition d blck elements. Do we have to transfer the electrons of excited state to the vacant orbitals and then count unpaired electons??????????

Transition elements have free d-orbital which helps them to have a no. of valencies.
but before understanding method to count covalency one must know the meaning of covalency,

Covalency is the no. of valence electrons available in atom to form the covalent bond.

To count the covalency first write the electronic configuration of the element.
for example:
Ground state of Vanadium: [Ar]4s²3d³
Now, excited state of Vanadium: [Ar]4s¹3d⁴

Now count the no. of half filled orbitals which are available to accept the electrons to form the covalent bond here we have 5.

Hence, to know the max covalency of an element you have count the no. of unpaired electrons in the excited state.