I think in this particular occasion, I really am the best choice for this job.
I'm obviously a programmer, but also a very capable mechanic. It's a side-effect of being a motorcycle and car enthusiast. I've worked with wheels and tires in the past, so I know all about wheel fitments (PCD, offset, width) as well as tire sizes (width/profile percentage/diameter) etc.
I'm sorry to tell you, but you've just wasted your money in that Shopify theme! Ask for a refund and initiate a chargeback on the grounds of miss-selling and deception.
Shopify, Volution and all the others are complete waste of time and money! They are useless platforms for amateurs who don't know anything about web technologies.
To be fair, they are OK if you are only selling 10-20 simple products, but again only for amateurs, because there are better, more efficient, and much cheaper ways to do this as well.
Do you have a link to your ebay and amazon shops?
I'd like to have a look if you don't mind.
Also, would you be willing to disclose your last years P&L?
Let me know,
Best Regards