90% of that is 344W, so if I was coaching myself then I would start outside or inside non-Erg with something like 6 x (2min @ 335-350W and 3-min rest). After that workout I would take the average of work intervals, and use that for next anaerobic stamina/repeatability workout. Also in the next workout I might try and reduce from 3-min rest down to 2-min. Wouldn’t drop below 1:1 ratio if the goal was working on repeatability, so doing 2-min on and 1-min off is not something I’m familiar with. All that said, I would start with increasing capacity before doing these stamina / repeatability workouts.
Growing anaerobic capacity / power is a different workout, involving an all-out efforts and enough time to recharge before doing the next all-out effort. Each effort would be between 30 seconds and 2-min.
Re: how to improve… I’m not a coach, but have one. Personally if self-coached I would start with doing some capacity work, to increase glycolytic power and total anaerobic capacity. Then work on repeatability / stamina. Growing anaerobic capacity involves really hard all-out efforts, and takes a lot out of me. But I’ve done it in the past, then used Wed night worlds to work on repeatability / stamina. It works.
AFAIK those are some classic approaches and workouts. You should really discuss with your coach.