I run the app under Windows 10 so YMMV. There is a dotted representation of the "hamburger" menu for the station you are currently listening to. Select this and select 'Edit Station'.
You will see the 'Add Variety' link; sorry I put the red ring a little high. Click on this and you will get . . .
The Add Variety dialog box where you can add artist, artists with bands, bands, composers, etc.
This will add the selected artists or whatever to the station you started from. HTH