How can I convert a muffin recipe to make crumpets?
English muffins and crumpets are very similar, the only difference being that crumpets are wetter to allow the bubbles to rise out of the side off the heat. Without seeing a specific recipe, it's hard to know exactly what adjustments to make, as some muffin recipes are also quite wet. 

If you think your muffin dough is wet enough, you could just try cooking it as crumpets. If it doesn't bubble correctly on top, try making it a little bit wetter until it works.