My White Rodgers IF95-1291 series is blowing out only cold air how do I fix it?

Your White Rodgers IF95-1291 is a thermostat,the control that tells your furnace or heatpump or both to come on. It doesn`t blow air,hot or cold. You need to find your furnace find out what kind, electric/gas/oil
Then get the name brand and maybe a model number, look it over and try to tell us what its doing and not doing,, get back to us,asap and we try to help