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Best advice I ever had about changing between different tuba pitches came from Jim Gourlay (Currently MD at River City Brass but he played for the BBC Symphony Orchestra in the UK and conducted the brass band I played in).

His advice was: play all of them every day - even if it's just 10 minutes each but spend the most time on the one that's least comfortable.

Second this advice, just do it and you will get better in time.

I learned playing F by treating the bass clef staff as tenor clef. Doing that that way i could use my C fingerings, plus it gave me an opportunity to cover for the occasional trombone part that still used tenor clef. You just have to remember to add a sharp (like faking knowing Eb fingerings by changing clefs and adding 3 sharps). Yea, it's easier for me to think different note names than think different fingerings for the same note name. YMMV

But, more importantly, why isn't the plural of clef => cleves? Like leaf => leaves.

There was a session at the Army Tuba Conference this year that touches on this subject in the context of “doubling”. https://youtu.be/8Y-tP1MkeBA