Sorry, I think I didn't explained properly. I mean, I don't know how to write my own license.
I just want something simple, saying "don't distribute please", but I have no idea how to make it, or even if I need to make it. I thought maybe there is some standard license like that. On Unreal Market there is one, but it's crafted for the Unreal Market.
On the web I see a lot of advice saying "ask your lawyer". Well, where I live there is no such a thing like "my lawyer" :) There are lawyers of course, but they cost so much it's totally over the board for a $10 asset pack.