Madrid

The best way is to download the CityMapper app and follow its instructions when you arrive at Atocha.

Thank you for your prompt response I believe I can take the metro Cercanius commuter train C1 or C10 from Atocha just trying to confirm if this is correct as well if this is the best mode of transportation given I believe there is also a bus which makes the journey!

I believe your information is incorrect. CityMapper gives several options, but not Cercanias trains.

Both Atocha and Plaza Eliptica are on the Metro, but you'd need to change trains. I don't know whether it's the fastest option (as you said, there are buses), but the Metro map indicates you could take Metro Line 1 south to Pacifico and switch to Line 6 traveling clockwise to Plaza Eliptica. That looks like the fastest route if you take the Metro. I haven't been to Madrid since 2016 and don't remember the escalator/elevator situation in Metro stations, which could be a factor if you have significant luggage; with heavy bags, a single bus ride might well be preferable.

One handy feature of the CityMapper app is that it tells you which exit to take from Metro stations that have more than one, and then in which direction to walk--though that may not be an issue at Plaza Eliptica.