Audit Assistant keeps the prior year balances from the rolled forward current year, along with the subtotals created and risk assessments that may be brought forward.
So when you are importing the new year it is better to leave all that there rather than using "clear all" and starting again.
On your second year Excel or CSV import we suggest you delete the entire "prior year column" from the import file (delete including heading - not zeros or blanks).
If you leave the prior year column in the import file any differences in the new file totals will over-write the old one (which is why you can't use zeros or blanks). You may wish to do this if you are concerned that the prior year trial balance figures in Audit Assistant are inaccurate for some reason, otherwise leave as they are to ensure that the financial statements have the comparatives correct.
Any new accounts not in the prior year column will be put at the top of the Trial Balance ready to be dragged or edited into the correct section.
Also see Trial Balance Import