try

main.py

@@ -3,6 +3,7 @@ from flask import render_template, redirect, url_for, flash
 from flask_login import LoginManager, login_user, logout_user, login_required, current_user
 
 import moviedb_func
+from moviedb_func import delete_movie_by_id
 
 app = flask.Flask(__name__)
 app.secret_key = "Start1234!"
@@ -121,6 +122,15 @@ def save_manual():
 
     return redirect("/")
 
+@app.route("/delete_movie/<int:movie_id>", methods=["POST"])
+@login_required
+def delete_movie(movie_id):
+    if moviedb_func.delete_movie_by_id(movie_id):
+        flash("Film erfolgreich gelöscht!")
+    else:
+        flash("Fehler beim Löschen des Films.")
+    return redirect(url_for("index"))
+
 
 if __name__ == "__main__":
     moviedb_func.create_movie_database()