Anything that would help build a strong probability theory background.

Assuming you have some freshman-college math literacy, here are a few great introductory books to Probability theory:

    Introduction To Probability by D. Bertsekas & J. Tsitsiklis 

https://www.amazon.com/Introduction-Probability-2nd-Dimitri-...

    Elementary Probability Theory: With Stochastic Processes and an Introduction to Mathematical Finance  by K. L. Chung & F. AitSahlia  

https://www.amazon.com/Elementary-Probability-Theory-Introdu...

    An Introduction to Probability Theory and Its Applications Vol. 1 by W. Feller 

https://www.amazon.com/Introduction-Probability-Theory-Appli...

I'm sure there are some great video lectures on the subject as well, but unfortunately I can't point you to any relevant material since textbooks is what I used when I was in college. But if I had to guess, the latest relevant MIT OCW course that has video lectures available would be sufficient.

I always think that learning probability can not only help you to gain more intuition when dealing with scientific relative subjects but also empower you to think the daily life things in a different way. I recommend Introduction of probability [1] since it's easy to study and provides great free video lectures [2].

[1] - https://www.amazon.com/Introduction-Probability-Dimitri-P-Be...

[2] - https://ocw.mit.edu/resources/res-6-012-introduction-to-prob...

Introduction to Probability, 2nd Edition by Dimitri P. Bertsekas, John N. Tsitsiklis. It is textbook for EECS Probability course at MIT and very well written for beginners.

Additionally, there are video lectures available on MIT OCW which mirror this book closely.

https://www.amazon.com/Introduction-Probability-2nd-Dimitri-...

While I did take courses in probability, linear algebra, and lots of calculus, until recently, I forgot most of the probability and all of the linear algebra I learned in school. As for calculus, I only remembered how to take basic derivatives. In any case, I've been spending the past month brushing up on my linear algebra and probability, and it's been a struggle, but now that I'm motivated and under no time pressure to relearn the material, I find it way more fascinating than I did in college. In fact, I skipped tons of my linear algebra classes because I thought the subject was dry and dull. I also rushed through my probability and stats homework just so I could get a good grade on them. I think if you're motivated, and you can do basic math, you should be able to educate yourself in calculus, probability, and linear algebra. It'll be a struggle, but with motivation, you'll be able to pick up the concepts.

for probability and stats: https://www.amazon.com/Introduction-Probability-2nd-Dimitri-...

for linear algebra: https://www.amazon.com/Coding-Matrix-Algebra-Applications-Co...

this was my college calculus textbook: https://www.amazon.com/Calculus-7th-James-Stewart/dp/0538497.... I can't comment if it was good or not because by college, I had taken calculus twice so it was all a refresher

best of luck! You sound educated enough (yes, I'm judging from the couple sentences you wrote) that I think you won't have any problems acquiring math knowledge with persistence.