Replacing words from a sentence
It'd be easier to separate this into two parts. First, we can do all the word transformations using map and a single word switcher:

(define (switch-word word)
  (cond ((equal? word 'I) 'you)
        ((equal? word 'me) 'you)
        ((equal? word 'Me) 'you)
        ((equal? word 'you) 'me)
        ((equal? word 'You) 'me)
        (else word)))

(define (switch sentence)
    (map switch-word sentence))'


That handles all the word swapping in one go, without having to write the iteration code yourself. 

Now all we need to do is change the first word from me to I, if appropriate:

(define (me-to-I word)
    (if (equal? word 'me) 'I word))

(define (switch sentence)
    (let ((switched (map switch-word sentence)))
        (cons (me-to-I (car switched)) (cdr switched))))