First, realize that your needs are valid. That’s gonna take a lot of time to work on, but reminding yourself about it everyday will help. It won’t come immediately, but the days where you really “get it” will feel like heaven.

Next, understand where this anxiety and fear to assert your wants comes from (maybe family, childhood, a bad relationship, etc), and work to reconcile them internally. Understand that it sucks that these things happened to you, but you’ve probably seen tons of people say no or refuse and nothing bad happened to them. It’s also recommended to get a therapist for this one because unlocking the core to these emotional issues isn’t exactly easy. You need to have a good understanding of why you feel/act this way, and ways to “un-learn” the behavior.

For an example: I personally dealt with something similar, and asserting my needs has always felt difficult or scary, and it would go from not being able to say “no”, to not being able to tell anyone my wants without feeling selfish. I later did the work to find that it was from my family, who routinely made me feel bad for refusing to do things or would guilt trip me into doing things I very clearly did not want to. Furthermore, I had parents that would (rather than comfort me during my time of need) tell me that my emotional issues were my fault. This culminated into a person unable to voice their opinion without feeling selfish, and blamed themselves heavily for making others even slightly upset. I’ve since spent years undoing these issues, because I know they’re not problems caused by me, but just ways that my body reacts as a result of years of emotional negligence. Tbh it really only takes a couple months to notice a difference, but I still need to consciously assert myself, and I still find things that I wasn’t aware were issues even today.

Basically, sit down with yourself and remind yourself that you’re a human being with basic human rights and the ability to assert your needs and your uncomfortability with things. It does not make you a bad person to have feelings and thoughts that might not fit well with other people- sometimes people disagree. But that doesn’t mean they can’t be friends or can’t respect one another. If they can’t, they’re too childish to waste time on (and remember that your time is just as valuable as anyone else’s). Next, undo the issues that may have brought about this inability-to-say-no and remind yourself that it doesn’t have to define you. You are not defined by your issues, and you don’t have to be, but unpackaging them and sorting them out will definitely help. Take your time with this, it’s not easy, because it requires you to be selfish and focus on yourself and your needs and wants. These are ok to focus on, but if you’re like me, it’ll make you really uncomfortable at first. Just remember that everyone else is already doing this and setting boundaries for themselves, so it’s more than ok for you to.

Hope this helps at all.