code: public function replace($search, $replace, $caseSensitivity = true)
      {
          if ($caseSensitivity) {
              $this->string = str_replace($search, $replace, $this->string);
          } else {
              $this->string = str_ireplace($search, $replace, $this->string);
          }
  
          return $this;
      }
docs: Replaces every occurrence of the string $search with the string $replace.
  
  @param  string $search
  @param  string $replace
  @param  boolean $caseSensitivity
  @return StringHelper