I can probably talk someone through this. Basically you want it to be big and bulky for your felt project. and if you plan to felt the i-cord you'll want to make it about 1/4 longer than the finished piece.
You start by casting on 3 or 4 or 5 stitches, depending on whether you want it to be thin, big, or bulky. If you used two strands of yarn throughout your felted piece then use 3 strands of yarn to make the i-cord (holding 3 strands together) this gives it thicker fullness when felted.
I'll use 5 for an example. Cast on 5, (if you use double pointed needles) move the 5 stitches to the opposite end of the needle they are on, so that your working yarn is on the last (left) cast on, then knit the five cast on stitches, bringing your working yarn that is actually on your last cast on, over to the first stitch. The first row doesn't reveal the i-cord, but after a few rows you begin to see the cord form, pull the stitches relatively tight as you go.
2nd row and each following row slide the stitches to the other end of the needle, and use the empty needle to knit again in the same fashion. It sounds a little complicated, but once you do these steps you'll see an i-cord forming.
If you don't have double pointed needles, or some broken circular needles, use two knitting needles but after the cast on slip all 5 stitches to the left needle, knit a row and slip all 5 stitches to the left needle, repeat till the cord is the length you desire,