Best way to remove fan noise (?)

Dear Community,

An amateur needs your kind support. I have a sound file, three people recorded (in German) with a H4n recorder in a lecture hall, with two rather loud fans in the background. It's easy to remove the fan noise via sound reduction, yet a very unsettling artificial echo remains.

I wonder what may be the best way to achieve the best audio quality, according to your experience?

Thank you very much in advance,

Oliver