A huge amount of attractiveness is about self care. So if you have well cut hair, nicely shaped eyebrows, well kept nails and skin, that is a big start.
Then getting fit is a massive bonus. You don't have to have a perfectly proportioned body or be tall, but if you are toned, have good posture and move with energy, then these things are very attractive.
Finally, dressing in an interesting way that makes the best of your best features and carefully works with your least good features also helps.
You can easily do something about all of these and it will make a HUGE difference.
If your self-image doesn't improve after that, you would do well to find a therapist who specialises in body dysmorphia. IME thinking of yourself as plain has far more to do with self-esteem than actual features. But it can have a lot to do with self care. If that is poor, then you are putting yourself at a disadvantage.
Why don't you try an experiment for a month?
Do online yoga classes every day (e.g. Adriene (If these cost money there are loads of free ones by her and others on you tube, including Jessamyne Stanley who is a plus size yoga teacher - go for her more active opnes, though as some of hers are just about gentle stretching and breathing.)
do 10-30 mins bodyweight, HIIT or handweights/kettlebell training every day too. Again there are loads of online free videos. Just type 10 minute beginners bodyweight into you tube and take your pick, then increase gardually to 15 mins, 20 etc.
Get a hair cut, get your nails done and eyebrows shaped.
Start a skincare regime that suits your skin type. Doesn't have to be loads of money or products. Ask for advise on Style & Beauty.
Chuck out all clothes that make you feel like a lump. Buy some clothes wiht a bit of colour, modern necklines, in fabrics that feel good against your skin. Wear them every day. Style & beauty will help you find what suits your shape.
Even if you have very little money, you can get brows done at Superdrug, do your own skin and nails, get hair done by a junior stylist or mobile hairdresser who are often much more reasopnably proced. If you are in a big city, it can be free at a training academy (but takes hours!)
You could try affirmations - e.g. I like and accept myself and take good care of myself - said every day when you wake up, when you look in the mirror and when you go to bed,. You don't have to believe it, you just have to say it calmly without sneering at yourself as you do it. It can help replace critical internal commentary.
See how you feel in a month if you have done this.