What is the procedure to dry out Fenugreek leaves?
The biggest cause of mould or fungus is humidity (moisure, dampness, water in the air) and the leaves by nature will produce this as they dry. After all, the drying process is removing water from the plant.

As long as you dry the herbs in an area with plenty of air circulation (to avoid humidity build up and take away any moisture as the leaves dry) you should be fine.

Make sure the herbs aren't bunched together, spread them out on a tray so the air can circulate around them. Turn them over regularly - every day or every 6 hours or so so they can dry evenly.

Remove any damaged/crushed/torn leaves or stems where mould can get a hold and spread.

Also remember just because the outside leaves stems may feel dry, the insides may not be, so give them longer to dry out than you think.