But there's nothing you CAN do to help (not without the asspull of the crucible). It's an existential threat. Not a military one.
Personally, I would have recommended a two front strategy:
(strategy A would be the open and obvious one, while providing cover for B )
A. Trying to overwhelm single Reaper capital ships, preferably by using special mobile ambush groups led by one or more dreadnoughts (which ideally remain at long range) and reinforced by a large number of speedy frigate / corvette wolf-packs, armed with the heaviest weapons you can mount of them and little else. (shields and armor on a frigate are useless anyway against reapers, so keep only anti-fighter defenses to fight off oculi)
The second part of the first front is to systematically lure large numbers of Reapers into specific systems, and then repeat the Alpha relay incident somehow, and blow the entire system with everything in it.
The third part is research, try to find vulnerabilities in Reapers and exploit them, or develop more effective weapons against them.
(example: A flying gun - a dreadnought's main gun with only the minimal construction to enable it to travel and shoot accurately,
might be somewhat effective for long range ambush sniper groups focused on single Reapers.)
B. Run.
Essentially organize a secret exodus (or hide like Javik's group - hey they almost succeeded if not for indoctrinated traitors), either out of the MW, or to an area that for some reason the Reapers don't like to visits, if because of space hazards or whatever. With the hope that you can live to fight another day and take back the MW probably by developing appropriate technology during the time until the next cycle. (for all their power the Reapers seem rather stagnant technologically)