To turn off automatic relists when completing a new listing, you clear the tick box on the Business listing form. It is just below the Returns options section on the form I looked at.
You may have to switch to the Business listing tool from the Standard one, and you may have to use a laptop/PC, not a phone or the app.
I think auto relist is compulsory on some recent offers. I think you can't turn it off if you have used one of those offers.
For live listings, go to the ““More Actions”” dropdown menu to the right of the item in your Active selling list and select ‘End Auto Relist’.
One of your items is ending very soon. You may not be able to revise the listing so near the end of the auction. You could let the item relist and then revise it as for new listings.
Regarding the message you have received about selling outside of eBay, what exactly did it say?
If you have attempted to exchange contact details with a prospective buyer, eBay don't allow that unless the buyer has committed to pay by going through eBay Checkout (but they don't have to pay yet).
Any attempt to exchange contact details before the buyer has committed to buy can lead to your account and the buyer's account being suspended.
https://www.ebay.co.uk/help/policies/payment-policies/offers-buy-sell-outside-ebay-policy?id=4272
