Any tips on making sub-30 in 50 meter short course free?

I (18M) am a semi-competitive swimmer and I’m looking to improve my freestyle time. I currently have a ~33s 50 meter freestyle. I’m hoping to get that down to ~28s. It should probably be noted that I have a lung condition that makes taking in and holding deep breaths difficult. Do you all have any tips on improving freestyle? I’m open to any suggestions (but I am keen on calisthenic, flip turn, and/or breathing tips).

Cheers!

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