Keep (Retain) DropDownList selection throughout application in ASP.Net Core MVC

Hi, I am first time using Asp.Net Core MVC 3.1 and I am not sure how to implement below requirement in Core MVC.

I have 3 dropdowns in my application in as a filter. User selects DDL items and click on button, data related to selected DDL items is displayed in grid.

Requirement: Upon selecting dropdown items, the selected item shall remain throughout the application (like a session in Asp.Net) until user re-selects or closes the application

Startup.cs:

public class Startup
{
	public void ConfigureServices(IServiceCollection services)
	{
		services.AddSession(options => {
			options.IdleTimeout = TimeSpan.FromMinutes(1);//You can set Time  
		});
	}

	public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
	{
		app.UseSession();
	}
}

ViewModel.cs

namespace SLB.ETLWebApp.ViewModel
{
    public class MappingWellViewModel
    {
        public string StudyId { get; set; }
        public SelectList StudyList { get; set; }

        public string ScenarioId { get; set; }
        public SelectList ScenarioList { get; set; }

        public string ProjectId { get; set; }
        public SelectList ProjectList { get; set; }
	}
}

Index.view:

Filters:
<select id="ddlStudy" class="form-control col-md-8" onchange="GetScenario(this.value);"
   asp-items="@Model.StudyList">
   <option value="">--Please Select--</option>
</select>
 
<select id="ddlScenario" class="form-control col-md-8" name="ddlScenario">
   <option value="">--Please Select--</option>
</select>
 
<select id="ddlProject" class="form-control col-md-8"
   asp-items="@Model.ProjectList">
   <option value="">--Please Select--</option>
</select>
 
<button id="btnFilter" style="border: none;background-color: transparent;" onclick="filterDataTable();">
   <img src="@Url.Content("~/images/Apply.png")" style="height:30px;width:30px;" />
</button>

Controller:

using Microsoft.AspNetCore.Http;

public IActionResult Index()
{
	MappingWellViewModel mappingWellViewModel = new MappingWellViewModel();

	mappingWellViewModel.StudyList = BindStudyDDL();
	mappingWellViewModel.ProjectList = BindProjectDDL();

	return View(mappingWellViewModel);
}

public SelectList BindStudyDDL()
{
	var data = (from x in _repository.GetAllMappingDetails().ToList()
				join z in _repository.GetScenarioDDL().ToList() on x.FdpStudy equals z.StudyName
				orderby z.StudyName
				select new
				{
					StudyId = z.StudyId,
					StudyName = x.FdpStudy
				}).Distinct().OrderBy(x => x.StudyName).ToList();

	var ddlStudyList = new SelectList(data, "StudyId", "StudyName");

	return ddlStudyList;
}

public JsonResult BindScenarioDDLByStudyId(string selectedStudyId)
{
	var data = (from x in _repository.GetAllMappingDetails().ToList()
				join w in _repository.GetScenarioDDL().ToList() on x.FdpScenario equals w.CombinedName
				where w.StudyId == selectedStudyId
				orderby w.ScenarioName
				select new
				{
					ScenarioId = w.ScenarioId,
					ScenarioName = w.ScenarioDisplayId + " | " + w.ScenarioName
				}).Distinct().OrderBy(x => x.ScenarioName).ToList();

	return Json(data);
}

public SelectList BindProjectDDL()
{
	var data = (from x in _repository.GetAllMappingDetails().ToList()
				join y in _repository.GetProjectDDL().ToList() on x.PearlProject equals y.ProjectName
				orderby y.ProjectName
				select new
				{
					ProjectId = y.ProjectId,
					ProjectName = x.PearlProject
				}).Distinct().OrderBy(x => x.ProjectName).ToList();

	var ddlProjectList = new SelectList(data, "ProjectId", "ProjectName");

	return ddlProjectList;
}

Requirement: Upon selecting dropdown item, the selected item shall maintain throughout the application until user re-selects or closes the application.

I am not sure how to set session inside controller code. 

Example code:

// Set Session.
HttpContext.Session.SetString("StudyDDL", "StudyItem1"); //here "StudyItem1" is study dropdown selected value
HttpContext.Session.SetString("ScenarioDDL", "ScenarioItem1"); //here "ScenarioItem1" is scenario dropdown selected value
HttpContext.Session.SetString("ProjectDDL", "ProjectItem1"); //here "ProjectItem1" is project dropdown selected value

Please guide me/help me to achieve the requirement, please. I am a bit confused.

Thank you in advance