If you are working in an IDE I can help, but if you are in MCreator I cannot help. I do not EVER recommend using MCreator. It is always better to actually learn the concept instead of downloading a program that does it for you. It will also give you a new skill if you learn actual modding. Then, you'll be able to code in Java. If you do decide to use an IDE, reply to this comment and I will help you. I do not think MCreator can even make potions, so sorry.