There will be no automatic calculation of progress from the supporting key result to the existing key result. If you would like the new key result to automatically progress up, you should either convert the key result to an objective or manually update the progress of your existing key result.
Add a key result or supporting objective with cascading goals
Navigate to the Goals page.
Click on the Your goals preset filter.
Expand the objective and then click on the key result you would like to add support to.
Click Insert objective or Insert key result to open the goal context panel.