I don't know this software, so can't tell you how to fix it, but it's clearly a bone problem.
When you add the penis to the model, it try to follow the position of a bone that is missing. And like it's missing, it send this part of the penis somewhere on the infinite.
Either the figure for the penis is corrupted, or you need to firstly change the skeleton for the model, in order to use one that have the bones for the penis.