How can I upcycle soap bar scraps?

Unless they are competing, you can put them all together to form a larger bar. Gently boil, simmering for a few minutes. Drain in a metal colander with a wooden spoon. Pour into a plastic wrap lined bowl then remove when cooled & set.

slice a small slit in a sponge & put your soap pieces into the sponge or you can put soap pieces into a clean panty hose & use to lather your hands

I make liquid soap from full bars, scraps even better. My son has this weird texture thing about bar soap, it grosses him out. I grate the bars, 3 or 4 at a time, add a gallon or so of water and simmer until they are dissolved. I use old body wash bottles to store. I like that I don't have the extra plastic to try and recycle and my son is not freaking out about having to touch a bar of soap....

You can treat glycerine based soaps like melt and pout and turn them into new bars

https://www.hometalk.com/diy/-39041056

Here is an idea https://www.pinterest.com/pin/178666310201711077/