here's a quote from my blog that explains how to perform "The Fishing Line Method" of tongue splitting.
Fishing Line Method - Yes, you can split your own tongue with just fishing line. I would imagine this is the most common way tongues are split as no doctor is required. The only requirement is a healed tongue piercing and some thin monofilament fishing line.
Thread the line through the hole where the piercing barbel usually goes. Feed the line through and line it up with the center of the tip of your tongue. Tie the fishing line as tight as you can bear, and be sure to knot the line several times to avoid slippage. Remove the excess fishing line and leave it alone for three to four days. At that time, remove the existing fishing line and retie the tongue as tight as you can bear. Continue this process for several weeks and you will slowly split your tongue.
The tongue may not split completely using the fishing line method but the process can easily be completed with a quick swipe of a razor.
You can of course see the whole tongue splitting article HERE
Hope that helps