In order to change a crisp number to fuzzy number, it is advisable to use expert opinion or you can generate a fuzzy normal distribution with a mean of the crips value and variance 0 or small value. "Genetic algorithm based fuzzy stochastic transportation programming problem with continuous random variables" is my paper in OPSEARCH, you can get the details. I hope this will help!
Most of the academicians used the expert base fuzzification procedure by conducting questionnaires or surveys. Other fuzzification methods are also available. The intuition method, Inference method, Rank Ordering method, Neural Networks method, Genetic Algorithm method, Angular Fuzzy Sets method, and Inductive Reasoning method are some of them.