In this task, you need to replace a letter in the sentence with another given letter.

Example Input: Sentence: 'vita mix blender with something in it already blended'. Replace the letter 'b' with 'a' in the sentence.
Example Output: vita mix alender with something in it already alended

Example Input: Sentence: 'a small bird perched on a open window'. Replace the letter 'e' with 'r' in the sentence.
Example Output: a small bird prrchrd on a oprn window

Example Input: Sentence: 'many people are standing at the wavy beach area'. Replace the letter 'o' with 'i' in the sentence.
Example Output:
many peiple are standing at the wavy beach area