If you want to reconcile GSTR2A with GSTR3B, there is no specific option available for it in the BUSY. Therefore, you have to check manually either date-wise or month-wise. Below are the steps you can follow:
Step 1: Go to the Display menu.
Step 2: Click on GST Report and then on the GST Return option.
Step 3: Open the GSTR2 report, and export it to Excel.
Step 4: Similarly, click on the GSTR3B option and export it to Excel.
Step 5: You can then either reconcile manually from there or from the BUSY itself.