Добавил проверку на POST запросы в контроллер

Polyclinic/PolyclinicWebAppImplementer/Controllers/HomeController.cs

@@ -17,9 +17,18 @@ namespace PolyclinicWebAppImplementer.Controllers
         {
             return View();
         }
+        [HttpGet]
+        [HttpPost]
         public IActionResult Course()
         {
-            return View();
+            if (HttpContext.Request.Method == "POST")
+            {
+                return Redirect("~/Home/Courses");
+            }
+            else
+            {
+                return View();
+            }
         }
         public IActionResult Courses()
         {
@@ -27,7 +36,14 @@ namespace PolyclinicWebAppImplementer.Controllers
         }
         public IActionResult Diagnose()
         {
-            return View();
+            if (HttpContext.Request.Method == "POST")
+            {
+                return Redirect("~/Home/Diagnoses");
+            }
+            else
+            {
+                return View();
+            }
         }
 
         public IActionResult Diagnoses()
@@ -36,7 +52,14 @@ namespace PolyclinicWebAppImplementer.Controllers
         }
         public IActionResult Symptom()
         {
-            return View();
+            if (HttpContext.Request.Method == "POST")
+            {
+                return Redirect("~/Home/Symptomes");
+            }
+            else
+            {
+                return View();
+            }
         }
         public IActionResult Symptomes()
         {

Polyclinic/PolyclinicWebAppImplementer/Views/Home/Course.cshtml

@@ -4,7 +4,7 @@
 @{
     ViewBag.SelectedSiteMenuItem = SiteMenuItems.Course;
 }
-<form class="d-flex flex-column">
+<form class="d-flex flex-column" method="post">
     <div class="row mb-5">
         <div class="col-3">Количество дней:</div>
         <div class="col-8"><input type="number" id="daysCount" name="daysCount" /></div>
@@ -21,16 +21,16 @@
         <div class="col-3">Рецепт:</div>
         <div class="col-8">
             <select id="recipeId" name="recipeId">
-                <option>Выберите рецепт</option>
+                <option value="">Выберите рецепт</option>
                 <option value="0">Какой-то рецепт</option>
             </select>
         </div>
     </div>
     <div class="row mb-5">
         <div class="col-4">
-            <a class="btn btn-success">
+            <button class="btn btn-success" type="submit">
                 Сохранить
-            </a>
+            </button>
             <a class="btn btn-danger">
                 Отмена
             </a>