Retrieve Webform submission data from database
Easiest is probably to preprocess the webform's new submission, load the desired submission, and then pre-populate your fields. I doubt that this is built-in.
fe
&lt;?php
function HOOK_webform_submission_form_alter(array &amp;$form, FormStateInterface $form_state, $form_id) {
  if ($form['#webform_id'] == 'your_webfom') {
    $form['elements']['your_element']['#default_value'] = $your_value;
  }
}

There may be several ways by not-coding, but using modules.
LMGTFY - https://www.drupal.org/forum/support/post-installation/2021-02-01/how-to-use-webforms-submissions-in-other-forms

Install the 'Webform Views Integration' module.
Create the view for display submissions of the 'Client' webform.
Add to the view the 'Entity Reference' display and add the 'Name' field (or any field you want to see on the 'Project' webform).
Click on the 'Settings' and check the field that will use for serach.
In the 'Client' webform select the following reference method: 'View: Filter by an entity reference view'.
Select the view created by you from the 'View used to select the entities' list.

The screenshots of the example:

https://ibb.co/ZJxgK9w
https://ibb.co/C6sxCFv
https://ibb.co/mFWDCTX
https://ibb.co/QcwYYm6