Hi,
In the backend, if you have the product_id, you can simply open a product and change the value of the "cid[]=" in the url.
You will edit the wanted product and you will be able to see where this product is (in which category etc).
You will be able to move it in a specific category and see it in your backend listing, and finally, delete it if you want.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.