If it hurts
If it hurts the tell your partner it does. Do not keep doing something and it hurts you try something different. If you like the pain then take it slow and keep trying but if you don’t want to continue then try something different.
If your using a toy and it hurts then try adding more lube and or using a finger or something else to loosen you up. Let your partner arouse you and it works better.
Sometimes you have to start small. Doesn’t matter how big you are use to things can hurt and cause problems.
Get comfortable use lots of lube and that should work. Never force anyone they are not comfortable with because it can cause problems and it can discourage them into doing it again if they dislike it.