Navigate to the Balances page in the sidebar

Use the dropdown to group by bank

Scroll down to the institution that contains the account(s) that you'd like to update

Click the 3 circles icon on the far right, then select "Update Balances"

Select the applicable Date Range and Balance Type (options include Opening Available, Closing Available, Opening Ledger, Closing Ledger, and Current Available)

Type or copy and paste the desired values

Once done, click the blue "Done" button in the top right corner