To add or change an App's Advanced Features, you must first be in the 'Configure' section and scroll down to the 'Advanced Features' Template. Once there you can set the Advanced Features:
NOTE: This is not the in-depth article on this matter, for that please see here.
Under this Template you can set a 'Record User Identifier Field' via a Field within the App. This is then used instead of the Softools assigned Record ID. This can be good practice if there is likely going to be lots of data Imported into the App without it first having been Exported.
This is because when data (or Records) get Exported from Softools, the first column in the Export spreadsheet is for the Record ID, meaning that each following column (Field) and its data is assigned to a specific Record (per row). Hence if you attempt to Import Records without these IDs the platform does not know which Records the changes are intended for. Yet, if you set your own Record ID Field you can choose something more simple and more uniform in comparison to the Softools generated Record ID, this way the platform can still recognize what data belongs to which Records. If it were 'RAID' for example this is much easier to reference and keep track of when making new Imports without Exporting first.
Make sure to click the 'Save' button when making any changes in order for them to be added to the next app version. Once you have made all the changes you need to an application you are then ready to publish it to workspace.