To use Goal Seek for single periods:
From any Strategic Finance view, select Analysis, then What if Analysis, then Goal Seek.
In By Changing Account, select the source account affecting the goal.
This account must be related to the goal account through a formula. To view account relationships to determine if there is such a formula, see Using Analyze.
In In Period and To, enter the years to change the source account.
Either use the returned adjustments in your mode or reject the results.