From the example:
M → N (+1)
A → Z (−1)
N → O (+1)
G → H (+1)
O → Q (+2)
These shifts are not consistent, so there isn't a unique coding rule that can be applied to "PEACH."
Could you check whether the code is correct? For example, confirm whether "MANGO → NZOHQ" is exactly as written. Once the rule is clear, I can determine the code for PEACH.