In the latest Designer, there is a Modeling tab called What If, which lets us add a New Interactive Parameter. We’ll need to specify its Name, Data Type, Min & Max values, Default and internally PowerBI will create a table with 2 columns. The first is a column with all the possible values for the parameter. It’s very useful for putting in a slider for viewers to use when using the report. The second column is a measure which will be equal to the currently selected value and we use this as a reference in our calculations.
PowerBI will add a slider to your page: