How do you blay f# on e# clarinet??

I'm a music teacher and I've never heard of an e# clarinet... did you mean Eb? Press the left hand first finger down only for an F#, the low one of the staff. The high f# on the staff would need the octave key/thumb, 123 on left hand and the third finger on the right hand. Look up a fingering chart, I'm sure there are some online.