Crear cuenta
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<input type="checkbox">
<input type="text">
</body>
</html>
<script>
document.querySelector("input[type=checkbox]").addEventListener("change", ()=>{
document.querySelector("input[type=text]").value="hola";
});
</script>
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
</head>
<body>
<input type="checkbox">
<input type="text">
</body>
</html>
<script>
document.querySelector("input[type=checkbox]").addEventListener("change", ()=>{
let v=document.querySelector("input[type=text]");
if (v.value=="hola") {
v.value="";
} else {
v.value="hola";
}});
</script>