Adjust start date when schedule has logic applied to it

Hello everyone, I am a construction student using asta to build a schedule for a project I am working on. Now, I have built the entire schedule start to finish, but unfortunetly I have forgotten to add my preconstruction tasks, which, are required for my project. I established the start date (Notice to Proceed) for 10/12/2018 and proceeded with my schedule logic. I would like to have the preconstruction tasks starting on 8/27/2018 and move in logical order on the schedule. However, every time I reschedule, it moves the start date of my precon tasks up to 10/12/2018 regardless of constraints removed and changing the start date in bar chart format tab. Please let me know if anyone can help. Thank you - Austin