We recommend that you purchase a plug, as shown in the photo, for your sink. The hole is drilled with this plug as an example. Other plugs will probably also fit, but with this one you are sure.
The plug costs only € 40, - incl. VAT and is of excellent quality.
If you prefer to buy a plug somewhere else yourself, keep in mind that the plug may not be lockable. After all, a petrified wood wash basin has no "overflow".