While some of these YouTube 'fixes' may get one out of the ditch temporarily, please don't count on these as permanent repairs.
It's been a long time back, maybe a decade ago, I tried one of these 'reflow' tutorials & while it initially worked, failed for the final time in less than a week.
Professional repair wouldn't be worth the money, can outright purchase a top line card instead. The only thing I can suggest would be to carefully disassemble, clean very well, reapply thermal paste & if that doesn't work, then the reflow option is in your hands. Yet to do it right requires professional equipment which most legit PC shops doesn't have.
A suggestion & fair warning, it's time to be looking for a new(er) GPU. Be wary of eBay while looking, chances are if the seller says the card has not been overclocked, used for mining/heavy gaming, the buyer is about to get burned. For the most part, the mining craze is over (GPU prices are dropping) & there's lots of these being unloaded on eBay, Craiglist & other sites. Sometimes at cost equal or more than a newer card if on promo.
It's time to sign up for promos at Newegg & other sites & be on the lookout for your next GPU. Considering you've had this one for years as open box & has served you well, have came out good. I suggest if you do buy another, to be sure & clean on a regular schedule, along with the rest of your computer. Those dust bunnies builds up & causes overheating, sometimes to the point where you'll be in the same boat again. Warranties often doesn't cover negligence, air dusters are low in cost & very effective to clean with.