"I can't invest; I don't know how." "I don't know how to get out of debt." "Budgeting doesn't make sense to me." A simple and powerful way to shift your perspective is to put "yet" at the end of each sentence.
Failure's a dirty word when you have a fixed mindset. However, not only is failure a natural part of life, but it's also (from the perspective of a growth mindset) a cornerstone of progress. Replace the word failing with learning.
Our brains can change throughout life too. A rapidly growing body of research shows they're amazingly malleable. Your brain can and will change for the better (which lends extra credence to the power of yet).