1 : Comment voulez-vous que je m'y prenne ?
= "How do you want me to go about it?"
The 1st sentence is straightforward enough, but the exact meaning in the 2nd throws me off.
Also, how would you paraphrase the 2nd if it didn’t occur to you to use this expression?
2 : Comment voulez-vous qu’ils aient eu le temps de commettre un tel crime ?