How can i get rid of a mild stutter?

How can i get rid of a mild stutter? Im 15 and its hard ti explain but i have days where i talk normally and barely stutter, and days where i cant speak without having to repeat myself 3 times. Some peopel dont mind but i used tl get told that i talk too fast and when i have to repeat myself on one of those days i stutter even more to the point where i just give up and say „nevermind“. When i have to present at school i dont stutter at all i just ahve the problem of speaking too fast. Also i find it harder to speak clearly without stuttering or talking too fast in loud or crowded environments. What are some hacks to fix this and why do i have that?