You should be pushing yourself to use the heaviest weight you can as safely and efficiently as possible. It’s okay to adjust the weights set to set on given days if you are having trouble completing the rep ranges. The main point is that you are breathing heavy and can still perform proper movement patterns.
The purpose of this training block is to work on functional hypertrophy, conditioning into resistance training and introduction into your first real strength phase. You will see development in strength, lean muscle growth and the ability lift heavier weights that will give you the confidence to push yourself in new ways.