I just want to know the process. :)

Use a on the desired pet :) Reborn potions restock in the Magic Box and sometimes in the Token Shop!

Use a on them. The item can be bought from User Shops, but also restocks in the Magic Box.

Occasionally it restocks in the Token Shop, but I think your best bet is buying it from another user unless you're really in no rush to change your pet. [edit] Ninja'd and I didn't even add any useful information. Sorry about that.

http://subeta.net/forums.php/read/141578/Frequently-Asked-Questions-Answers has the information you need. Do a Find on Reborn.

If you just want a Reborn pet and don't care what species, you can also snag one in Adopt R Us and you can zap this color.