Three Fish has it.
Having a curtain that can be pulled over one of the large reflective surfaces could cut the reverberation significantly. Finding a solution in the tech side of things will be tricky if not impossible, other than getting people closer to the microphone.
If there is a single presenter, you could look at using a microphone with a Cardioid polar response, i.e it’s most sensitive to sound hitting it from the front. Strong room reflections come from other directions (generally).
Conference mics are generally omni-directional and cannot distinguish between what is direct speech sound and reflections of the speech from room surfaces. Hence the solution is to reduce the strength of the reflections compared to the direct sound. The best way to do this is to treat the room or get people much closer to the mic. The former will give the best results, as you’ll have to rely on people to remember to be close to the mic for the latter. (perhaps a much smaller conference table would work for that?)