The new modern tv box receives the tv signal from a modem/wifi.
The output to tv on the box is via hdmi or USB.
The tv is old, it now receives tv signal from a coaxial cable.
Is a converter from HDMI to coaxial cable exists?
Look for other inputs on your TV. Coaxial is not used for this. Most likely there will be SCART input, and i think its best to ask your provider for a box that has a scart output.