Chronotherm Iv Plus & Install Where Do I Find The Furnace Filter For My Heating System & How To Replace It?

Where do I find the furnace filter for my heating system & how to replace it? - chronotherm iv plus & install

We have a system of gas central heating in our house and is maintained by a thermostat More Braemar IV This thermostat, that the word filter is blinking. I do not know exactly what that means, but I suspect that clean, or something that matters. Can someone tell me where I can find the filter too? What works and where it normally? Even when (and if) I think, as it is clean?

Thanks