Step 1: Draw the inner angle and diagonal (according to the nature of the diamond, the diagonal should be the bisector of the inner angle);

Step 2: Make the middle vertical line of the diagonal line, which intersects with both sides of the inner corner;

Step 3: Connect these two intersections with the other endpoint of the known diagonal.

It is known that the quadrilateral surrounded by two sides of the inner angle plus these two connected sides is a diamond.