I think I'm trying to find the C in an RSA cipher to find the key for an aes_128_ecb cipher, can anyone tell me if I'm on the right track?
I think you should review how RSA encryption and decryption work.

You are given all the elements you need:

$P = C^d \mod N$

You know $d$, you know $p$, $q$, and thus $pq = N$. Usually people use $e$ to the encryption exponent and $d$ for the decryption exponent, but from what you said, $d$ is being used to encrypt.

You can recover $C$ with $P^u \mod N$, where $u$ solves:

$ud = 1 \mod (p-1)(q-1)$

Can you figure it out from there? (Hint: The Extended Euclidean algorithm will help.)