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

Example Input: Sentence: 'a large elephant standing outside beside a tree'. Replace the letter 'e' with 'y' in the sentence.
Example Output: a largy ylyphant standing outsidy bysidy a tryy

Example Input: Sentence: 'a skier with his legs covered in snow lifts one of his feet to stamp it'. Replace the letter 's' with 'y' in the sentence.
Example Output: a ykier with hiy legy covered in ynow lifty one of hiy feet to ytamp it

Example Input: Sentence: 'a living room couch with a display of large mirror and flowers'. Replace the letter 't' with 'e' in the sentence.
Example Output:
a living room couch wieh a display of large mirror and flowers