Epic frequently offers free skins during seasonal events like Winterfest or special collaborations.
These changes are "client-side," meaning only you can see the new skin. Other players in your lobby or match will still see you wearing your original outfit. fortnite-skin-swapper-free-download
Many "free download" links for skin swappers are fronts for malware, keyloggers, or phishing scripts designed to steal your account credentials. Epic frequently offers free skins during seasonal events