Can I Add Another Router To Small Office Network That Is Experiencing Poor Signal Upstairs - Currently Have Two Routers And A Switch Connected

Hi everyone, thanks in advance for any help! I am a complete novice at this, but am trying to help out!

I work in a small office that is two stories, in the far corner of the upstairs the wi-fi is extremely slow. We currently have an AT&T modem with two routers and a switch connected to it. The area that has slow internet does have a wall plate with an active ethernet port, can I simply connect another router to this port that the people upstairs can then connect to that would have better signal than when they connect to the routers downstairs? Although there are wall plates in many of the offices, almost everyone in the other offices uses wi-fi without any issues.

It’s also been suggested that range extenders may help. I was also just told that a wireless access point may be the way to go and am going to look into that as an option.

If this would not work, any suggestions on a simple way to make this work? It's really only three people in one large room that are experiencing issues.

Thanks again for any help!