Making bespoke skins in PUBG may rely on the context of which you refer to official in-game skins or self-made changes:
Authoritative way (facilitated by PUBG):
PUBG does not support the ability of players to upload custom skins. Skins are acquired via in-game events, crates, the Workshop or during official PUBG skin design contest, through designs posted.
Not official/modding (not a good idea):
PUBG has a terms of service that can be infringed by the creation or use of custom skin via mods or third-party software, which can also lead to the banning of accounts.