Here's how you can find the filter option in Swipes
Press on the small circle button next to the 'add' button. You'll then get a menu with an easy access to settings, search, tag & filter and multi-select.
To filter by tag, select the filter button > choose a tag and press it. All other tasks will be hidden. You'll only see the tasks related to the selected tag across all areas - schedule, focus (middle), completed.