After selecting Sell, go top right of the listing page, and click on Advanced listing tool, ignore that it says its for business and high volume sellers only, it isn't it is for everyone to use.
Then, you can de select that Auto relist, by making sure the little auto relist box remains unticked at bottom of your listing page.
For existing listings, go far right of the item More Actions >> End auto relist.
If this cannot be done on an app or phone, you need to switch to a laptop / PC / browser to manage this.
