Hi,
If I understand is correctly, are you looking for when or which user made a changes to the system with custom app, and you want to track those changes, so there ware multiple ways as follows.
1. You can use Github or Azure Devops to track the changes made in your app with using of Branches.
2. Inside the APP you can ask them to record the changes write somewhere in the README.md file what has been done and when.
or if you are looking for when the data has been changed so you can go with the Change log setup it will let you understand what table, and which field's value when and which user user has changed. but Keep in mind it can consume more space as much as the table will be ON with this setup.
Thanks.
