Please solve the programming task below using a self-contained code snippet in a markdown code block.

The hash of a 0-indexed string s of length k, given integers p and m, is computed using the following function:

hash(s, p, m) = (val(s[0]) * p0 + val(s[1]) * p1 + ... + val(s[k-1]) * pk-1) mod m.

Where val(s[i]) represents the index of s[i] in the alphabet from val('a') = 1 to val('z') = 26.
You are given a string s and the integers power, modulo, k, and hashValue. Return sub, the first substring of s of length k such that hash(sub, power, modulo) == hashValue.
The test cases will be generated such that an answer always exists.
A substring is a contiguous non-empty sequence of characters within a string.
 
Please complete the following python code precisely:
```python
class Solution:
    def subStrHash(self, s: str, power: int, modulo: int, k: int, hashValue: int) -> str:
```