...a little dress. Obviously meant for a toddler girl. Not exactly what Oliver was aiming for, but he did decide to try on whatever he found. He pulls off his clothes and tries to pull on the dress. It, of course, doesn't fit at all and he feels quite stupid for believing in magic rings.
Suddenly, he feels his whole body contracting as he shoots backwards through adulthood and then his teenage years then puberty and into early childhood. He also feels the odd sensation of his penis retracting into his body as his organs rearrange themselves. The dress soon easily slips over "her" form.
It seems the changes are too quick for the ring. Even though it was shrinking with her, it slips off her finger before it catches up fully with her now pudgy fingers and rolls under the side of the fitting room. Oliver gasps as she watches it exit sight.
She wants to pursue the ring immediately, but curiosity overwhelms her and she looks in the mirror first. Staring back is a girl around 3 years old who looks absolutely adorable in her new dress. She can't help but smile at the image, even with the ring very temporarily lost it had done its job. Once she retrieves it she can be anything she wants.