Did you read the documentation about debugging your native app?
This part explains how to get the log files out of a device
Hope it helps!
In addition to Lennart's answer, there also a additional way of capturing client errors or log messages from nanoflows and getting them in your database. Be sure to check out the solution described by Sylvia Wentzel in a webinar from MXW2020. It starts around 8:40 https://www.capegroep.nl/how-to-build-a-scan-app-with-native-mobile/
The solution is to write these messages to a log entity and sync them to your backend. Make sure to apply the correct sync settings to keep the sync lightweight.