I worked on a asp.net core 1.1 project a while ago and use in projetc AutoMapper.
in asp.net core 1.1, I add services.AddAutoMapper() in startup file :<
services.AddAutoMapper()
If you are using AspNet Core 2.2 and AutoMapper.Extensions.Microsoft.DependencyInjection v6.1 You need to use in Startup file
services.AddAutoMapper(typeof(Startup));