[William Hughey]

If you can not hang acustic dampning material (egg crate, sheets ,carpet) on the walls you might want to try sampling the talent, and feeding a small ammount of audio back into the room 180 degrees out of phase. This will cancell some of the echo or some of the audio frequencies. This will depend on the room size and placement of the monitor speaker. Audio delay is also a nice thing to have on hand when “trying” to cancel echo or acoustic echo in a room electronically instead of mechanically.
Sample the audio either from the mic or second mic, delay the audio just a bit (a few ms, 65 ms is good by routing the mic through an adjustable audio delay board) then to a amp and monitor speaker (placement in the room will have the greatest effect) invert the phase of the sampled audio (switch the polarity of the speaker around not great but effective on a budget) adjust the delay, audio level, and placement of speaker for best effect.
This is not easy it is not an exact science you can try it with out spending thousands of dollars on computer programs and equipment. The best way to stop acoustic echo in a room is with sound absorbing material or sound dampening material, Foam packing material that resembles a egg container with peeks and valleys will work as well as the expensive stuff made for the studio. If you cannot hang something on the walls try the phase echo cancellation experiment.