I'm an undergraduate math major, recently I've written a paper about approximation by neural networks in a theoretical settings because I really like the mathematics involved in neural networks. It is a paper mainly based on another paper, for your information, 'Optimal Approximation with Sparsely Connected Deep Neural Networks' by Bölcskei et al.
What I've done is not something innovative at all. I proved two results from the original paper because the author only gave a hint on how to prove the theorems, and I thought it will be a good idea to explore more. As a result, I found some other research papers which helped me to gave the two proofs in great detail.
Now my paper is nearly complete, I just have to choose which journal to submit my paper, then do a little adjustment based on their requirements, it will then be done. However, I'm not confident enough to publish my paper to, for example, the SIAM Journal or the IEEE Journal, because they would expect research works with more originality and innovation. How do I find and evaluate suitable journals for my type of research paper?