You cannot convert a live "Buy Now Only" listing into an auction (or vice versa); you must relist the item to change the primary format.
When you list an item for sale, you will reach a section for pricing. trade me add buy now
To add a price to your Trade Me listing, you can either include it while creating a new auction or add it to an existing live auction that hasn't met its reserve. Adding Buy Now to a New Listing You cannot convert a live "Buy Now Only"
You generally cannot add a Buy Now price to a live auction if it has already received bids that meet the reserve. Adding Buy Now to a New Listing You
In a standard auction, the Buy Now option disappears once the reserve price is met through bidding. If there is no reserve, it disappears after the very first bid.