There are three ways you can do this in gantterAi:
From the General tab in Project Settings
Open Project settings, and under the “General” tab, change the “Plan from” from the Start date to Finish date.Changing the Dependency in the Predecessors menu to “Finish-to-start”
Open Task settings by double-clicking on the task that is being worked on. Select Predecessors, which is the third tab under Task settings). From there, click on the task that you will want to finish before starting the task you are working on.
Remember to think of this as a sentence: (a task that is checked off) needs to finish to start (a task that is highlighted).Changing your Constraint in the Advanced menu to “As late as Possible”
While under Task settings of the highlighted task, click on the “Advanced” tab to view constraints used on the task in question. You will then need to change the constraint to “As late as Possible”.