All service agreements should be set up properly before beginning to backload reserve balances.
Once the service agreement and the reserve are set up in ESC, go to Agreements → Backload Agreement Reserve. All agreements that have Reserve setup will appear in this list along with the current balance for that agreement.
If you do not see an agreement here, it is because it is not set up to use Reserve. Recall the Memorized Transaction screen for that service agreement and check Active. Enter the opening balance in the Amount field and the correct balance should appear in the New Balance field. You will only be able to edit the Amount and Memo field.
After all reserve amounts are entered, the Service Agreement Reserve Reports from both ESC and your previous accounting package should match.