Control DC Motor with Arduino Uno WiFi Rev2 Html Slider Code
Here's an example of slider that changes a Servo speed,
In html page code you have to add this:

  &lt;div class="slidecontainer"&gt;
  &lt;input type="range" min="0" max="1023" value="512" class="slider" id="myRange"&gt;
  &lt;p&gt;Value: &lt;span id="demo"&gt;&lt;/span&gt;&lt;/p&gt;
&lt;/div&gt;

&lt;script&gt;
var slider = document.getElementById("myRange");

var output = document.getElementById("demo");

output.innerHTML = slider.value;

slider.onchange = function() {
  output.innerHTML = this.value;
  pwm_change(output.innerHTML);

}
function pwm_change(val) {
  var xhttp = new XMLHttpRequest();
  xhttp.open("GET", "setPWM?PWMval="+val, true);
     xhttp.send();
}
&lt;/script&gt;


In arduino you have to define handler like this:

void handle_pwm() {
 String  pwm_val = server.arg("PWMval"); // reading from slider on html pagae

 Serial.print("slider val: ");
 Serial.println(pwm_val);
int pwm_value = map(pwm_val.toInt(), 0, 1023, 0, 180); 
Servo.write(pwm_value);

server.send(200,"text/plane","0"); // handling the webpage update

}


And define servo and handler in Setup() section:

void setup(void){
....
Servo.attach(MotorPin,1000,2000);
server.on("/setPWM", handle_pwm);
....
 }