When adding steps to an Activated Checklist you can either add it at the end, or use the Insert Step feature to insert a step above or below the currently selected step.
To add a step either above or below an existing step, select the step and then choose the ellipsis (the 3 dots). It will show "More Actions" when you hover your cursor over it
When you click on it you will see the options "Insert Step Above" and "Insert Step Below" Select one based on where you need to add the step
For this exercise we'll add a step above.
The inserted step appears as a floating window ready for you to add the new step information
Also select the type of step you need it to be
Once the step is ready, hit enter on your keyboard and the new step will be placed (in this case) above the step you originally selected