Are there any good online courses on Internal Audit?

I am looking for a good course on internal audit. I have joined a mid sized firm recently. I do not get adequate guidance from my team leader before starting an internal audit. He just expects me to do the audit based on last year's working papers. I feel lost as to what am i supposed to do. I feel nervous while facing the client as they may ask questions which i may not be able to answer. Please share some good courses if you have done something yourself. I know CIA course but that is too expensive for me. I cannot afford it at present. I just want to improve my knowledge and skills on internal audit so that i can perform better at my work.