Help me in solving DEBUGPYU14 problem

help
,
1

My issue

please help to correct this code

My code

t = int(input())

for _ in range(t):
    n = int(input())
    s = input()

    s = list(s)

    for i in range(0, n-1, 2):
        s[i], s[i + 1] = s[i + 1], s[i]

    for i in range(n):
        if s[i] != 'z':
            s[i] = chr(ord('a') + ord('z') - ord(s[i]))

    encoded_message = ''.join(s)
    print(encoded_message)

Learning course: Python with Data structures
Problem Link: Practice Problem in - CodeChef