Data to be displayed on webapp based on condition selected from the input from google sheets

I have make a webapp for data capturing. If they select a option on webapp then one data value to be auto displayed on webapp from google sheets. I tried with some codes but not succeeds. Example if i select A or B or C or D then a value will insert inside the plan box which data stored in google sheets. Please suggest.

 .heading {
    margin-top: 20px;
    margin-bottom: 10px;
    text-align:center;
    color: black;
    font-size: 60%;
    height: 85px;
  }

<head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
    <base target="_top">
  </head>
  <body>
      <div class="heading">
        <h1><b>Data Monitoring</b></h1>
      </div>
  

      <div class="catg">
        <select id="Category">
        <option>A</option>
        <option>B</option>
        <option>C</option>
        <option>D</option>   
        </select>
      </div>


        <div class="mplan">
        <input id="mdata" type="number" value="0" min="0" oninput="validity.valid||(value='');">
        <label>Data Plan</label>
           
        </div>    
 
     <div class="actual">
        <input id="act" type="number">
        <label for="act">actual : </label>
      </div>

     <div class="sub">
        <button id="btn" type="submit" name="action">Submit
        </button>
     </div>
   
      
  </body>
</html>