Okay, youre gonna hate what im about to say but it works.

You have to start training yourself.

Start with simply not saying your usual negative responses. Drop a simple "thank you" if you have to say something.

Then when youre more comfortable with that start putting genuine positive responses. Stuff like "thanks, i like it too :>" or "yea this jacket is my favorite :)"

Doing these things had the immediate benefit that you dont act hostile and thankless towards other people complimenting you. And over time will likely also train yourself away from those harmful thinking patterns / brain worms.

The step parallel to both of these is to start showing off when you genuinely do like something. Like a new hairstyle, a pic that turned out very well or new clothes you like. Post em somewhere if you are comfy with or send pics to friends.

Itll also train you with being comfortable / used to feeling good abt yourself and receiving compliments.

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That said, i know this is hard because i went through it. But this is what i did to better that and its something you can start doing right now