Easy Python Solution
IntuitionApproachComplexity
Time complexity:

Space complexity:
Code
# Intuition
<!-- Describe your first thoughts on how to solve this problem. -->

# Approach
<!-- Describe your approach to solving the problem. -->

# Complexity
- Time complexity:
<!-- Add your time complexity here, e.g. $$O(n)$$ -->

- Space complexity:
<!-- Add your space complexity here, e.g. $$O(n)$$ -->

# Code
```python3 []
class Solution:
    def smallestString(self, s: str) -> str:
        s=list(s)
        n=len(s)
        i=0
        ##if string starting with 'a' dont cange and move to next, if list is full of 'a change the last 'a to z
        while i<n and s[i]=='a':
            i+=1
        if i==n:
            s[-1]='z'
        else:
        ##if character is not 'a' than change it to previous character
            while i<n and s[i]!='a':
                s[i]=chr(ord(s[i])-1)            
                i+=1
        return "".join(s)        
```
['Python3']