To use the FORECAST or TREND function in Excel you should follow these steps:

1. Create the table where you want your results to appear.
2. Enter data into the table.
3. In the cell that contains the predicted value, enter the FORECAST or TREND Function.
4. Click the cell with the FORECAST or TREND Function to activate it.
5. In the dialog box, select the known x-range and y-range and the new x-value.
6. Check that the new x-value in the Trend Function dialog box is correct.
7. Click OK.