Controllers.cs

// Version 1

namespace WebApiSwaggerVersion.Controllers.V1
{
    [ApiController]
    [Route("api/v1/[controller]")]
    public class WeatherForecastController : ControllerBase
    {...}
}

// Version 2

namespace WebApiSwaggerVersion.Controllers.V2
{
    [ApiController]
    [Route("api/v2/[controller]")]
    public class WeatherForecastController : ControllerBase
    {...}
}