Neither. You are not allowed to ask for reviews, or for reviews to be changed, or to refund the buyer in exchange for having the review removed which wouldn’t work anyways, the review stays even if the buyer cancels the order through CS after completion.
The buyer - according to the TOS- has the right to review the seller according to the experience they’ve made. I think in some cases if the buyer is actually lying in the review, you can ask CS to have the review removed but this is always a bit of a tricky subject, they will probably also quote the TOS on it.
I would leave it at that and move on, though you can respond to any review you receive which will be shown on your profile but the buyer doesn’t actually see it unless they go to your profile. You could respond mentioning that the client was difficult to deal with or something along the lines.
A 1 star review would always affect your ratings, may or may not lead to your ranking dropping and possibly can also decrease the number of requests / orders you receive temporarily. If you have still have the choice to do something about it, I’m not saying I would recommend it necessarily, but you could cancel the order before delivering so the buyer gets a refund and can’t write a negative review to begin with. But then you also don’t get paid and your order completion rate drops a bit.