Although there are a few rowing centered exercises which can be accomplished with dumbbells, I prefer to opt for a tougher work out and add some body weight to it. The basic spinal erector exercises are deadlifts and front squats. You can do dumbbell Romanian deadlifts, and that will help. https://hammer-strength-dumbbell89000.yomoblog.com/39741284/a-simple-key-for-hammer-strength-dumbbell-rack-unveiled