Inspect your repair, and ensure there are no further stitches to be made before cutting the threads. Then, make a double stitch at the final point, to secure the thread - there is no need to make a knot.

Carefully cut one loose thread...

... and then carefully cut the other loose thread.

Flatten down the edges of the repair and smooth the entire repaired area.

Tip: flatten item on a hard and flat surface, and use the rounded side of your darning egg or mushroom to firmly apply pressure on a circular motion to the repaired areas, to smooth down the edges.