html custom required message code example
Example 1: change input required text html
<input type="text" id="username" required placeholder="Enter Name"
oninvalid="this.setCustomValidity('Enter User Name Here')"
oninput="this.setCustomValidity('')" />
Example 2: how to change input required message
<input class="form-control" type="email" required="" placeholder="username"
oninvalid="this.setCustomValidity('Please Enter valid email')"
oninput="setCustomValidity('')"></input>