It can be tricky to print a return label if you don't have a printer.
However, you can usually get items printed at your local library or print shop, or forward your email to a friend with a printer.
It is better to be proactive and get things sorted rather than rely on empty promises from a seller and lose your money.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)