I am building a website for an online store I wanted to know if there is any app where I can upload products to my store from eBay ?

not from my store on ebay. thank you

The Wix Corvid Forum is for all code related issues on your site, if you simply want answers about apps, then please contact Wix Support instead.
https://support.wix.com/en/about-wix/contacting-wix-support

If you can get an api from ebay that allows you to grab products to use then you can just use Wix Fetch or Wix HTTP Functions to get your products.
https://support.wix.com/en/article/corvid-accessing-third-party-services-with-the-fetch-api
https://support.wix.com/en/article/corvid-exposing-a-site-api-with-http-functions

Otherwise, you can try to download your products as a csv file and import them into your Wix Stores.
https://support.wix.com/en/wix-stores/setting-up-your-store

However, if you can’t do that then you will need to manually get them all into your datasets.