Add a regression line

Graphs
     Chart Builder
          Gallery: Scatter/Dot
               Drag the Simple Scatter chart to the Chart preview
                Drag xxx from the variable list to the "X-axis" box
                Drag yyy from the variable list to the "Y-axis" box
     OK

double-click
Chart Editor

Elements
     Fit Line at Total

(multiple regression)
Options
     Reference Line from Equation
          Reference Line: Custom Equation: k + (bx)
          Apply
Close the Chart Editor