[edit] メソッド名の変更をしました

src/main/java/com/example/demo/controller/BookLendController.java

@@ -5,7 +5,7 @@ import org.springframework.web.bind.annotation.PostMapping;
 @Controller
 public class BookLendController {
 		@PostMapping("/bookLend")
-		public String welcome() {
+		public String bookLend() {
 			return "bookLend";
 		}