1) An iron and ironing board
2) fabric glue
Step 1: Split open the tie
Since a single strand of thread holds the whole tie together, once you snip that strand, you should be able to pull it out without continuing to cut it, but this takes some practice. If you need to, just cut the thread as you go.
Split the tie all the way up to the skinny part.
Step 2: Trim the felt insert
Flip the skinny end of the tie onto the felt. You'll use this as a guide for trimming the felt. (Ensure that the tie is at least wide enough to hide the tail of the tie behind itself.)
Use a marker to mark off the excess felt.
Lift the felt away from the tie and iron the tie flat.
Tuck the skinnified felt back into the silk pocket.
Step 3: Fold the tie over the felt and trim excess material
Use the iron to put a new crease into the tie as you fold. Fold and iron in portions as you move up the tie.
After you've folded one side and ironed it flat, trim any excess material.
Fold the other side of the tie over the felt. Trim excess material, but still leave enough to recreate the folded pleat (you can see this in the last photo included with this step). This extra fold of material is not absolutely necessary but it will give the finished tie a more polished look.