Make it, Fix it, Renovate it, Rehabilitate it - as long as you’ve done some part of it yourself, share!
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I'd recommend just going for a new wheel and tire. Harbor Freight or your local equivalent probably has one that will fit with a solid tire under $20 and never having to worry about flats or airing it up is worth it.
There's also a solid chance the tire is really old and doesn't have much life left anyway. By the time you patch it a couple times, you've probably wasted more than $20 of your time.
It might fill the tire and make it round but it probably won't hold much weight. If it does hold weight it would probably be a rough ride to push that thing around anything that isn't smooth ground. A tire patch like @darkwing_duck@sh.itjust.works suggested or a plug would probably give better results.