If you have a computer, then you have everything you need to do what I did. You just need to download the
Reaper DAW. Its free to try, and not expensive to buy the license.
I've done something similar to what you do, doing some recordings on my Zoom R24. I then pull the SD card, and move the files to my computer, and pull them into my Reaper DAW. I can then make any modifications I want, assuming that the effects in the Zoom were insufficient, and mix down to the final track.
For reverb, my favorites are the Bricasti M7 impulse files that were widely posted a few years ago. The Bricasti is a hardware reverb unit. The impulse files are samples that can be loaded into the ReaVerb plugin. It doesn't take a lot of reverb to make things open up. I used one called Vocal Chamber, and it was at -39dB. I like plate reverbs as well. Hall reverbs are usually too long for intimate sounding files. If I was doing choral or orchestral work, they might be more appropriate.
Since all I had was the final stereo master, all that could be done was to apply the effects to the stereo track. For you, that would be to put the effects on the master track, not the individuals.