The only way to install Celery on Wix is to link to your Celery shop URL unfortunately. The reason being that Wix does not allow for custom scripts.
Create a "Pre-Order" button anywhere within your Wix shop and click it. A pop up should appear with the option to set the link to your Celery shop URL.
Your Celery shop URL can be found inside your product builder.
Click Show me how and A link I can share.
Paste this URL into Wix and you're good to go!