You can use a conventional puncture repair kit if the hole isn't too big. I've used an automotive patch in the past; that was on a tyre with a tube, but I presume it will work with tubeless. The problem is that any trace of sealant will interfere with the action of the adhesive, so you need to make sure the area is very clean and dry. Also, sanding down the area around the hole will help. Annoying as it is, if the hole is very big I'd be inclined replace the tyre. Your safety isn't worth compromising on the cost of a new tyre.