Of good comprehensive programs, I can recommend the course of Denis Koshelev on the site LookLearn Very well-structured, non-trivial nutritional advice, and in general it is pleasant to study. Well, questions can be asked to the trainer in person directly on the site, he answers quickly. Such a good substitute for training with a personal trainer with the same result.
An interesting and useful exercise is walking on the buttocks. You have to sit on your ass, stretch your legs and move your legs back and forth. Find more details on the internet.
My favorite workouts are leg workouts, and my buttocks are my problem area in terms of muscle growth :)
The following exercises help: squats, deadlifts, lunges, glute bridge, back swing with weights, squats on one leg, plie squats, flexion-extension of the legs on the simulator, step on the bench.
Please note that all exercises with weights, and especially with a barbell, should be done under the guidance of a trainer at least until you work out the technique.
Here is an example of exercises you can do at home
P4P - exercises of any kind, of any level. They have a YouTube channel. Last year I did the NPY for almost two months - the result is there. But do not forget about nutrition - this is also important.
The only correct answer: regular and over a fairly long period of time.
Running will help to a certain extent, as well as cycling, "tighten" all the muscles in the legs.
For the buttocks Squats and lunges will do. With your own weight or with light weights (1.5 kilogram dumbbells).
But it is better to contact a qualified fitness trainer who will identify "problem" places and prescribe a course of exercises.