char str[] = {'A','B','C'};
        char *ptr(char strArr[3]);

        void main()
        {
         clrscr();
         *ptr(str);
         printf("%s",*ptr);
         getch();
        }

        char *ptr(char strArr[3])
        {
           char tempArr[3];
                for(int x=2; x>=0; x--)
                  {
                        for(int y=0;y<=2;y++)
                        tempArr[y]=strArr[x];
                  }
           return tempArr;
        }

rev.c:2: conio.h: No such file or directory

So I fixed that by removing the line altogether. Then the compiler said:

rev.c:7: warning: return type of `main' is not `int'
rev.c: In function `main':
rev.c:8: warning: implicit declaration of function `clrscr'
rev.c:9: warning: value computed is not used
rev.c:10: warning: char format, different type arg (arg 2)
rev.c:11: warning: implicit declaration of function `getch'
rev.c: In function `ptr':
rev.c:17: parse error before `int'
rev.c:17: `x' undeclared (first use in this function)
rev.c:17: (Each undeclared identifier is reported only once
rev.c:17: for each function it appears in.)
rev.c:17: warning: statement with no effect
rev.c:17: parse error before `)'
rev.c:19: `y' undeclared (first use in this function)
rev.c:19: warning: statement with no effect
rev.c:19: parse error before `)'
rev.c:16: warning: unused variable `tempArr'
rev.c:14: warning: unused parameter `strArr'
rev.c:21: warning: control reaches end of non-void function

So I fixed all those, plus one or two bugs that I came across:

        #include <stdio.h>

        char *ptr(char strArr[3]);

        int main()
        {
         char str[4] = {'A','B','C'};
         char *rev = ptr(str);
         printf("%s\n", rev);
         puts("Press ENTER to continue.");
         getchar();
         return 0;
        }

        char *ptr(char strArr[3])
        {
           static char tempArr[3];
           int x;
           int y;
                for(x=2; x>=0; x--)
                  {
                        for(y=0;y<=2;y++)
                        tempArr[y]=strArr[x];
                  }
           return tempArr;
        }

All that's wrong now is:

1) your algorithm doesn't work;
2) your function only handles strings with three bytes in them.

To fix your algorithm is easy:

char *ptr(char strArr[3])
{
  static char tempArr[4] = {0};
  int x;
  for(x = 2; x >= 0; x--)
  {
    tempArr[2 - x] = strArr[x];
  }
  return tempArr;

#include <stdio.h>
char str[] = "ABCDE";
void rev(char *);
int main(void) {
  printf("Before: %s\n", str);
  rev(str);
  printf(" After: %s\n", str);
  return 0;

<snip>

2) tempArr is a pointer to a local variable which is destroyed when
the function ends. Therefore the returned value points to nothing
valid and contains garbage.

Just in case any newbies were reading.