Potentially found old Bitcoin I bought, how do I retrieve it?

Let me preface this post by saying I know virtually nothing about Bitcoin or crypto in general. Back in 2015, I purchased a small amount of Bitcoin on QuickBT (which shut down in 2018) to fund a sportsbook account I had. Long story short, I had some issues transferring the Bitcoin over and I'm not sure if I ever figured it out. I recently found the Bitcoin address in my emails and, based on a Bitcoin address lookup website, it still appears to be valid and contains what is now a decent chunk of coin.

My question for you guys is: How can I retrieve this Bitcoin? Is that even possible? All I have, to my knowledge, is the address.

Thanks in advance, and let me know if I didn't provide enough information.