Change between treble and bass clef if you choose practice at the start:
http://www.pedaplus.com/notegames/
Change to bass clef under the Change Clef drop down menu:
https://www.notationtraining.com/
Flashcards! Change clefs at the bottom of the page:
http://musicards.net/music_flash_cards/music_note_flashcards.html?Combobox1=treblenoledger