How to define the route data in asp.net core 6?

I am not able to get the actionContext since i am not able to configure RouteData i need help in how to define a routeData? I am passing the file name which is basically the filename for the view and along with it the model of the view which is to be redered.

 public class RazorViewsTemplateService : ITemplateService
    {
        private IRazorViewEngine _viewEngine;
        private readonly IServiceProvider _serviceProvider;
        private readonly ITempDataProvider _tempDataProvider;
        private readonly ILogger<RazorViewsTemplateService> _logger;
        

        public RazorViewsTemplateService(IRazorViewEngine viewEngine, IServiceProvider serviceProvider, ITempDataProvider tempDataProvider, ILogger<RazorViewsTemplateService> logger)
        {
            _viewEngine = viewEngine;
            _serviceProvider = serviceProvider;
            _tempDataProvider = tempDataProvider;
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
        }

        public async Task<string> RenderAsync<TViewModel>(string filename, TViewModel viewModel)
        {
            var httpContext = new DefaultHttpContext
            {
                RequestServices = _serviceProvider
            };

            var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

            await using var outputWriter = new StringWriter();
            var viewResult = _viewEngine.FindView(actionContext, filename, false);
            var viewDictionary = new ViewDataDictionary<TViewModel>(new EmptyModelMetadataProvider(), new ModelStateDictionary())
            {
                Model = viewModel
            };

            var tempDataDictionary = new TempDataDictionary(httpContext, _tempDataProvider);
            if (!viewResult.Success)
            {
                throw new KeyNotFoundException(
                    $"Could not render the HTML, because {filename} template does not exist");
            }

            try
            {
                var viewContext = new ViewContext(actionContext, viewResult.View, viewDictionary,
                    tempDataDictionary, outputWriter, new HtmlHelperOptions());

                await viewResult.View.RenderAsync(viewContext);
                return outputWriter.ToString();
            }
            catch (Exception ex)
            {
                _logger.LogError(ex, "Could not render the HTML because of an error");
                return string.Empty;
            }
        }
    }