In Settings -> System Configurations - Default Configurations.
Here you have the ability to set where or not you wish to have the Undo Button on the PortiaPro Mobile App set to:
1. Limit the Undo Button to one action (once) or all.
2. If the Undo Amount is set to Once. Then you need to Set the Undo Button visibility. The default is five seconds - this means the Undo Button will be visible for 5 seconds after the User has entered the data. Afterwards they will not be able to make a change.
To better understand the Undo Button - see Portia Pro Mobile App - Undo Button Article