Rower Looking for Off-Season Training

I’m a first year rower for my university looking to get into the heavyweight varsity boat. I’m 5’11 and ranging from 185-190lbs on a regular day. My 6km is a 22:30 and 2km is 6:51. I just need help looking at ideas of workouts I can do to help build my aerobic threshold. I’m looking to get in at least two a day; one being an erg workout, and the next focused on weights.

Any feedback would be nice.