You can tell others what you are okay with and not okay with. You can say “No” when someone does something you aren’t okay with, or use other ways to show that something isn’t okay.
For example, if someone tries to touch you, you can say “Don’t touch me.” or say “No!”. You could also just move away from that person.
Sometimes, you’ll be okay with something one day, then not be okay with it later. It is okay to change your mind, and to say “No!” even if you said “Yes” before. How you feel is important, and other people should respect your feelings.