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

Example Input: Sentence: 'closeup of two teddy bears in red scarves and a brown teddy bear'. Replace the letter 'i' with 'y' in the sentence.
Example Output: closeup of two teddy bears yn red scarves and a brown teddy bear

Example Input: Sentence: 'a fancy clock is lit up on the street'. Replace the letter 'o' with 'f' in the sentence.
Example Output: a fancy clfck is lit up fn the street

Example Input: Sentence: 'a dog that is laying down in the mud'. Replace the letter 'd' with 'w' in the sentence.
Example Output:
a wog that is laying wown in the muw