The input is a TRS but you bought a pretty niche looking product really. Can you still cancel it? If not return it.

Better buy this for same price https://www.amazon.com/Douk-Audio-Headphone-Amplifier-Desktop/dp/B08C2MKBGN/

all you need is a 3.5mm to RCA cable which you can find easily. Next step up would be something like a Fiio E10k but it's near double price at $75. And again next up is schiit modi/magni or jds atom/atom dac both around $200, but can also find them used of course.