How to rank a local business for another town?

I did SEO for a local german plumber in a city with a 30.000 population. No he would like to get listed in the neighbouring town which is 15km away too, obviously for the search term "plumber neighbouring-town-name"

What is the best approach to archive this? I thought about creating a new landing page for that specific keyword.. but I am not sure with which content I should fill that page?