Dead frets are deceptive. If you finger a note, pick the string and you get no tone or a buzzing flat sound, it means that the next fret up is the one that is giving you trouble. For example, if you play a note on the fifth fret and you get no sound at all or get bad tone, it means that the sixth fret is the problem. The sixth fret is higher than the fifth fret. The string bottoms out on it before it touches the fifth fret. You need to tap down the bad fret. This example can be applied anywhere on the guitar neck.
Place your index finger on the first string, which is the smallest string, at the first fret, and pluck the note. Ascend up the neck, playing each note at the next fret until you find the dead fret.
Place the block of wood on the next higher fret above the dead fret, just beside the smallest string. Tap on the block of wood three times with the hammer to drive the fret down.
Pluck the note at the dead fret. If the note is still dead, tap the wood block again until the note sounds clearly.
Pluck the biggest string on the dead fret. If the sound is dead on that string, place the block beside the biggest string on the same fret you are working on. Tap down on the fret on that side.
Pluck the note and listen. Tap again on the block, if needed, to get the note to ring out clear.
You might have to slightly pull the string aside to get the block of wood on the fret without pinching the string between the fret and the block.