Hi,
the easiest way to go is most likely Trimble UAV Ground Control:
https://play.google.com/store/apps/details?id=com.trimble.uavgroundcontrol&hl=en
This would be a one-time buy - its designed to work with Catalyst and allows exporting to csv (via marking all points - and then share either to say Dropbox, Google Driver or email).
Another option would be to download the SDK. The SDK has a sample application (called facade) that actually also stores a point log (not single points but essentially the position stream).
With a little bit of technical try and error its rather easy to change the facade to a simple 'store point' application.
Downside is that you need to side-load the apk and fiddle a bit around. Also the application is really a sample application for the facade interface (the easy-to-use API wrapper for Catalyst) so not exactly user friendly.
So these are the two simplest options that come to my mind.
Regards
Nico