Unfortunately, there's nothing you can do to remove the echo unless you know someone at the NSA :). However, using EQ to reduce certain frequencies where the echo is most predominant might help. Select the clip you want to filter then AUDIO FILTERS > APPLE > AUGraphicEQ. Double-click your clip and open the Filter Tab in the Viewer. You'll see many sliders you can tweak to try to reduce the echo. Start by cutting the low freqs and try boosting 3150Hz to 5kHz. You have to experiment because each space is different. You'll not remove the echo. Hopefully, you can reduce it's effect.
If you find settings that help, apply them to all your clips. Good luck.
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