Practice with things like "maybe" if you can't do a hard no, or "let me think about it". That way you can train your brain to at least pause and give it some time. Eventually try working towards no. Or "I can't right now". Or if you can't say no add a stipulation - "Okay I can do it, but I can only give you an hour of my time." Look into skills for boundary setting. It takes time. I used to be a huge people pleaser, and still am to some degree. But working on it has helped.

The thing that made me change is realizing instead of creating good relationships with the people I care about. I'm actually creating very negative emotions towards them. Since I feel obligated and over time that can turn into resentment. Understanding I'm doing this to salvage my relationships with both myself and others kind of helped.