FIRST you must cut a groove or trench deep enough and wide enough to accept the rosette and the black border strips on both sides of it. Carefully calculate your width and cut an outer and an inner circle. be sure that this cut only goes part way into the top board.
With the edges now established cut a number of inner circles to make it easy to scrape and clear out the trench. the drill press was set to stop at the proper depth so it will be easy to clean out the trench with a tiny chisel.
Now put the rosette into the trench with the backing side out. That will be sanded off. Cut and place the black purling around the circle getting it in nice and snug. You may want to have several thicknesses available or you use double layers if necessary to fill the gap. Once you have them fitted and cut, glue them in with super glue. The thin glue will flow around and under the rosette.
A 10/13/21 update. I am now working on instrument number 176, A Kasha tenor for a lady in California... I rarely have a ukulele for sale on my "available Instruments" page as I have many custom orders on my build list that must take precedence but check it once in a while. Occasionally someone will be unable to complete their purchase and their uke will be available and posted on the page.