Sims 4 Studio Miniatures (HELP)

[xX-FoXx]

Hi everybody and a happy new year!!
That's my 1st post, and i'm also creating my first clothes and tattoos in Sims 4 Studio.

It seems easy to use, it is quite intuitive, but even so I have some doubts.

 

1. I can not change the thumbnails. I mean, I upload a thumbnail in .png (for example, a nipple tattoo) but when I enter the game I see the image of the object I used in question (a ring). Can you help me with this and tell me in what format the image should be uploaded?

 

2. I am creating a nipple tattoo using "Create CAS Standalone", and then using a "ring finger". (So that it does not conflict with other elements). My question here is ... Am I replacing the object in question or creating a new one? Because when I enter the game, it appears with the ring finger image, as I said, and there is no copy of this (the original).
That's all by the moment. Thank you and I hope to share my creations with you very soon