how can I search for an input in a char, to replace it

in the function different i want to search for a specific letter which i set in a printf an scanf request in my main function. In the main function i also set the text and the letter which should be insert for the other letter.

#include <stdio.h>
#include <string.h>

int change (char *text, char search, char replace)
{
  int i=0;
  char help[40];

  sprintf(hilf,"%s",text);

  for(i=0; i<= strlen(help); i++) 
  {
    if(help[i]==search)
    {
      help[i]==replace;
    }
  }
}

int main()
{
  char name[40];
  int z, ne;

  printf("\nName: ");
  fgets(name, sizeof(name),stdin);

  printf("\nwhich sign do you want to replace: ");
  scanf("%i", &z);

  printf("\nnew sign: ");
  scanf("%i", &ne);

  change(name, z, ne);

  printf("\nchanged text is: %s", name);
}