Complete beginner signed up for a novice Triathlon

Hi there. I've been talked into taking part in a novice Tri which I think it's slightly shorter than a sprint. 400m swim, 21.6k bike, 2.6k run. I grew up swimming in a pool but it's been many many years. Cycling I'm fine with (did 65km between lunch & dinner just yesterday). I feel I could probably crawl the run. I just need advice.

Event is in the UK during "summer"