You can set the "Initial Balance" (sometimes referred to as a starting or an opening balance) when creating an account. The Initial Balance can also be amended at any time.
To amend the initial balance, select your account and choose Account > Edit Account.
In this window, you'll see your account details and you can amend the 'Initial Balance' field.
In the "Initial Balance" field you should enter the balance of your account, just before the earliest transaction in Moneydance.
For example, if the earliest transaction in your Moneydance account register is 1st January 2021, the initial balance amount is your bank account balance on 31st December 2020.
Moneydance can also calculate your Initial Balance.
For example, if your current checking account balance is $200, and the balance shown in Moneydance is $27.65, you can enter 200-27.65 (use the minus sign) in the Initial Balance field and hit enter. Moneydance will automatically calculate the proper Initial Balance.