"Service Call", a novelette by Philip K. Dick. Here is a plot summary from Philip K. Dick Review:
David Courtland, a researcher director for Pesco Paints, is studying the effects of the California heat on a new type of treated [shingles], when his work is interrupted by the doorbell. Courtland stops his work to attend to the door, finding who he assumes is a salesman at the door. Actually, he claims to be a repairman, sent to service Courtland’s swibble. Courtland [playfully] teases the repairman telling him he does not want his swibble fixed (in fact, Courtland has no idea what a swibble is). The repairman is deadly serious about his work and insists that the repair orders are for this house. Courtland shuts the door and continues his work, pondering what a swibble is. He was well read, but never heard of it before. He goes back to the door and finds the repair order [crumpled] on the floor. It reveals that the company the man works for was founded in 1963, well into the future. Courtland contacts his colleagues and asks them to come with a legal stenographer and tape recorder. He also contacts his boss, Pesbroke, and asks him to come over after telling him about the encounter with the repairman. He convinces Pesbroke that this is a once in a lifetime opportunity.
With the equipment set up, Courtland begins to brief his team. They will ask questions of the repairman in order to find out what a swibble and how it works. Now they only know they are widespread and a common feature of households. Soon the repairman comes back, but suggests coming another time because they have company. Although the repairman is amazed that this group seems to have no idea about swibbles, he starts to provide some answers. The swibbles are a bio-technology that were developed after a war in 1961. After a much larger war in 1975 which was fought between those who wanted swibbles and those who did not. The swibble-owners won that war. The main purpose of the swibble is to maintain ideological unity across the population by gradually shifting people’s ideological perspectives toward the norm. The 1975 [war] was fought by swibbles that rooted out the “Contrapersons.” War is eliminated because no one has any contrary point of view. Courtland and his colleagues point out a contradiction. If the swibbles shift people’s ideological perspective, and the people who repair the swibbles can adjust them, who is really in control? The repairman explains that all they do is keep the swibbles (which are alive) from dying by treating illnesses. With this knowledge in hand, they confess that they are from the past and send the repairman on his way.
It is not clear to the group how they can profit from this. Some think they should find the inventor of the swibble and kill him. During their discussions the door bell rings. At the door is an installment team, with a new generation swibbles for Courtland’s home.