<div class="form-outline datetimepicker myDatetime">

  <input type="text" class="form-control" id="datetimepickerDefault" />

  <label for="datetimepickerDefault" class="form-label">Select Date and Time</label>

</div>

<br>

<button class="btn btn-secondary" id="btn">

  Set default value

</button>

​

const btn = document.querySelector('#btn')

const dateTime = document.querySelector('.datetimepicker')

btn.addEventListener('click', () => {

    mdb.Datetimepicker.getInstance(dateTime).dispose()

​

    const myDatetimepicker = new mdb.Datetimepicker(document.querySelector('.myDatetime'), {

        defaultDate: "22/01/2019",

        defaultTime: "10:33 PM"

    })

})