This will not help anyone to help you
What we need is
See an example at App Inventor Tutorials and Examples: Inject | Pura Vida Apps
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no">
<meta name="author" content="https://puravidaapps.com">
<title>Test</title>
</head>
<body>
<div>
<form action="javascript:alert(document.getElementById('user').value + ' clicked the Submit button!');">
<label for="user">user:</label><br>
<input type="text" name="user" id="user" />
<br><br>
<label for="message">message:</label><br>
<input type="text" name="message" id="message" />
<br><br>
<input type="submit" id="submit" value="Submit" />
</form>
</div>
</body>
</html>
Taifun