Coding rehabilitation plan?

I have been writing code ever since I was 5 years old. Was pretty good at it. I became an entrepreneur 5 years ago and since last 3 years I haven't been coding. I have to take care of product, strategy etc. Now I am completely out of touch. How to get back to it? Obviously I have the coding aptitude, but I am out of touch with the current tools, APIs, function calls, libraries. What is the rehabilitation plan? Anybody who has gone through this?