If you pre ordered the Resident Evil 0 HD Remake then you have gained access to bonus outfits. You can use these as soon as start playing the game. There are multiple outfits for both characters to use! Check out wow to access the pre order outfits in Resident Evil 0 HD Remaster here!
How To Access The Pre Order Outfits In Resident Evil 0 HD Remaster
When you finally get control of Rebecca on the train, you can change her outfit. Go to the menu and then go over to the personal item slot. From here you can switch between your outfit stash and Rebecca’s mixing box. Use the the costume box and you will be taken to the menu to select an outfit for Rebecca. She starts with access to the STARS 2002 outfit, the Cheerlead4er outfit, the Western outfit and the Leather outfit. She can also use the Resident Evil 0 t-shirt if you want, switch to the t-shirt tab to access it.
You can do the same thing to Billy once you gain access to him. Switch his personal item and he will be able to choose a new outfit. Billy can use the Prisoner outfit, the Jacket outfit and the Wolf Force outfit. Billy does not get to use the t-shirt like Rebecca.
None of the outfits really fit with the situation but it is still fun to run around in them. Personally I went with the Wolf outfit for Billy and put Rebecca in the Leather outfit.