best filter to reduce echo?

You don't want to hear this: but it might be quicker and easier just to re-record if it's YOU doing the voiceover - in a room with dampening material hanging about e.g. bed duvets/blankets draped over the furniture or extended mike stands or tripods...

Traditionally you can't (easily) remove echoes with any filters.

Sadly, as you are discovering its next to impossible to reduce or eliminate echo and reverb once recorded.

Technically I suppose it might be possible if you had Altiverb and a profile of the room you recorded in to invert against the signal . . . . . but thats unlikely!

The best sensible suggestion I have is to use a "gate" plug in this will chop the signal at a preset volume level. So as a word ends you can limit the follow on.

You wont get rid of all the echo but you might lessen the effect, you could augment that with some EQ reducing the low end and high end to pull up the midrange EQ where voice normally resides.

For future reference a tie clip mic will give better audio in the field and acoustic foam placed behind the microphone facing the V/O speaker will give better results in the studio.

We just got back form eastern africa where we shot a documentary film.
We recorded over 80 hours of audio on mini disc recorders. Some of the audio was recorded poorly and contains excessive reverb (ambient)

There are things you can do like sharp EQ & denoise that will degrade the quality and reduce some echoing. BUT if you had the option to record, I'd do that. I wish I had that option

SP