How to create a private key using $n,e,d,p,q$ where $n$ is prime
You already stated the answer yourself: You know $N$ (which is prime by your assumption) and from the public key $e$ you can compute $d = e^{-1} \bmod N-1$, e.g. using the EEA.

With this $d$ you can then decrypt any ciphertext $c$ into the corresponding $m = c^d \bmod N$.