CapriRacer is exactly right in his/her tire patching advice.
Just for the record, there is no actual rule that says tires can only be replaced in pairs. Although it's generally a good idea, some tire stores make a big deal out of it and use it to sell tires that the customer may not really need. I'm an old guy and have sold tires at several different stores over the years and, for a time, was a service manager for a major tire brand. If you're dealing with relatively new tires, there's no reason you can't buy just one tire - as long as it matches the others.
You can also buy good used tires on the internet. I've used ebay seller VYC Tires before, but there are others. If you decide to do this, I'd advise you to invest in a tread depth gauge. They're cheap ($4.99 at Summit...
https://www.summitracing.com/parts/wmr-60504/overview/) and will allow you to buy a tire with close to the same amount of tread as what your damaged one had. You can also pick up a depth gauge at most retail auto parts stores at comparable prices. Just be sure to copy the info from the tire's sidewall to use in your search.
You'll need the tire brand, model and exact size. Here's an example:
Brand: Michelin
Model: Defender
Size: 205/55 R 16
In any case, good luck with your tires!