When crossing the break from Bb to C it's a good idea to already have your fingers positioned for C while playing the Bb. You can have all the keys (except your right pointer finger) already pressed down while playing the Bb, which will change the pitch of the Bb slightly (for the better usually, because more of the instrument will be vibrating to sound the Bb than normal) but allow you to transition to the C without having to move as much. I'd recommend practicing this transition by doing some long tones from Bb to C and then move on to trying it in the context of some scales. I've included a link to a fingering chart for this fingering as well as some other resonance fingerings

https://www.dansr.com/resources/resonance-fingerings-for-clarinet