Firstly navigate along the header pane to Modelling and see whether you have the drop down menu.

If you do not have this option and only have the numeric range then select file, Options and settings and then option

Select preview features then tick the field parameters box at the bottom.

Now close and reopen Power BI and now the option for field parameters is available.

If you do then select the fields option to then select the fields that you want to populate the parameter.