400m training help

Hey everyone, I am u16 and have previously specialised in 800m (pb of 2:08 last season) with a bit of 1500m and 400m (58s I think in u13 or14). However, this off-season I have really been trying to improve my 400m running. I’m training for an event in 4ish months and want to push a sub 55s. Any guidance and potential weekly plan would be greatly appreciated. Currently doing regular easy jog or tenpo on Saturday. Harder sprint sesh on Tuesday.