To change the logo, it is necessary to send a new version of the app to the Play Store (Android) and App Store (iOS).
For this we need to change it internally and then request a review from Google and Apple respectively.
Google usually releases the update the same day it is sent, while Apple has 2-3 days to evaluate and make the new version available.
Therefore, this isn't a change made immediately.
If you still have questions, check out our playlist of tutorials on Youtube.