On course.fast.ai there is a good online course to refresh your knowledge about Deep Learning.

Topics offered are how backpropagation is implemented in PyTorch using inline gradients, collaborative filtering using embedded techniques, working of convolutional neural network layers, tabular analysis with random forests and gradient accumulation to reduce memory footprint of GPUs.

For many topics there is an example in Excel that really explains what is going on under the hood of a complex deep learning model.

Last lesson is about Data Ethics and explains how through feedback loops implemented in social media our society got more polarized in important discussions.

There is a book for the course, which we recommend as well: