"My pinky collapses when I try to reach for octaves. What should I do? What do I do if my pinky collapses when I play slow and loud?" submitted by @chansamuel63

The pinky is naturally a weaker finger. We can strengthen it with drills and exercises like Hanon. 

1) First, we must check your form. The outer side of the pinky can be used, instead of just the point of the finger. Look at how you use the thumb - Finger 1. We do not use the point like Fingers 2, 3, and 4. We can use the side of our pinky (Finger 5) and ""hammer down"" as well as the point when we need to stretch octaves. This will require some practice.

2) If your pinky collapses, I highly recommend starting Hanon No. 31 to train your pinky strength. Go slow and play firmly. Press each key down.

https://easypianohacks.com/my-pinky-still-collapses-when-i-try-to-reach-for-octaves-what-should-i-do-what-do-i-do-if-my-pinky-collapses-when-i-play-slow-and-loud/