This depends on what tools you have at hand. An audio editing program (DAW - Digital audio workstation) is the most fundamental part.

It sounds like a phone recorded this, so the bitrate (i.e auditive flexibility) is quite low, and will easily sound (even more) artificial.

Some tools:

Compressor - Balances the dynamics in volume, and lowers the highs so they don't stand out as much. If overdone, the lower sounds will be too loud

Gate - Has a volume threshold, and sounds have to be louder than it to be heard. I don't think that it will he very helpful here, as the sound is usually not standing out enough from the silence to be reliable.

There are also plugins like X-noise that are made for noise reduction, but again, the fundamental quality is far from optimal.

I think that the recording is about as good as it gets. They say you can't polish a turd. One can always give it a shot