EDIT: Try what /u/hashbinbash said down below first. They seem to be talking from experience which is much better than my guesswork and it doesn't require you to buy anything.

This is a bit of guess work but here's what I think you need to do.

Short answer: Find a way to connect the atari to the top antenna connector. I can't identify it but can you plug the female part of an RCA cable to it? If yes, then it's simple a male RCA, a female-female RCA coupler would bridge the gap. SInce RCA is mostly associated with composite cables, you'll often find them in this format at your local "1-dollar shop" next to cheap earbuds and usb cables, I'm 90% sure theres nothing in the rubber between each coupler and you can just cut it to make it fit.

If a Female RCA cable doesn't fit... I don't don't what it is. Tell me and I can try to help you solve the mystery but without dimension or reference it's pretty hard to start looking.

Long answer: The two plugs on the left have the "antenna" symbol, so your atari is sending the right kind of signal for those connectors. These plugs are made to receive analog antenna signals, disregard anyone talking about composite and component signal, that the common fix but not the one your TV needs.

Now, I'm not sure exactly what the 75 ohm means, but normally those tell you the impedence the device must have. I'm really rusty on this and I,m not sure what impredence is anymore, but basically if your device doesn't have the right impedence, it doesn't work. The 75 om connector is probably for a less common type of signal which the atari doesn't produce. The atari has a "normal" antenna signal which should be compatible with the top plug.