To redeem Dress to Impress codes in Roblox, head to the dressing room then select the bottom left icon with a handbag and the word 'CODE' on it. This will open the DTI Codes window, which shows any items you've previously redeemed and has a text box at the top to enter new codes. Type them in then hit return or the tick icon, and if you've entered a valid code then you'll be presented with your new item(s), which you can then select from the DTI Codes window.