How does the enzyme Dicer function in the RISC complex?
Dicer is an endo-ribonuclease belonging to the RNAse-III class. Dicer is not a part of the RISC. It however helps in the formation of RISC by cleaving dsRNA or the stem of hairpin RNA on two ends which liberates a small dsRNA product. Then one of the strands is loaded into the RISC.

There are several reviews on this topic and there is a video as well which you can find on youtube.