Ow sorry next time don't deal to someone randomly the only problem is you deal to him outside from fiverr next time don't deal outside fiverr even there is a discount it isn't safe to deal without escrow.

I suggest enable RBF in your wallet as suggested above so that you can easily reverse the transaction.

Anyway, about the guide from post above check this https://blog.coinb.in/guide_double_spend_rbf