The parent ASIN is always listed in the URL - www.amazon.com/dp/B00DR5QTIM. To find the child ASINs in Amazon, click on the variation you want, then scroll down to the Product Details section where you should see the ASIN listed
Decide first whether you have time or not.
If you do, just search for free courses or videos, and manually explore the whole process.
If you are lacking time, you can enroll in a paid course and buy tools that will save you time on your search.
Here is a helpful guide on a private label (https://amzscout.net/blog/amazon-private-label/) and a great tutorial on how to start it on Amazon with only $3000. (https://www.youtube.com/watch?v=siAodJJDK\_4)