Go to KOHA administration > Global System Preferences and search for EnableBorrowerFiles.
On the left hand side of the patron account screen there will be several blue tabs. Click on the tab called Files.
This will take you to a new screen where files already attached to the patron account can be viewed or new ones can be added.
To upload the new file, add a description in the Description box and use the Choose file button to select a file from your device to upload.
Once the Description field has been filled in and the file has been added, click Upload file.
Uploaded files will appear in a table at the top of the page, which will include the name of the file, the type, the description defined when loading it and the date when the file was uploaded. To view the loaded file click the link under the Name column and a copy will be downloaded to your device.