Drill bit size differs from each throne, maybe
Old drum throne
Price of wood
Unscrew the top of the throne and take the cushion off then use the screw driver to take off the part that connects the cushion to the pole thing.
Get the piece of wood and cut it to the size you want it to be with the hand saw. Then get the drill with the drill bit that fits your throne and drill holes in the wood
Then screw the screws with the plate that connects the things. Into the drilled out hole with either the screw driver or the drill. Then put the piece of wood with the base plate onto the bottom of the throne then your done.