Trial balance import for any nominal account is easy but not the same for Retained Earnings.
You'll need to run a previous year's Profit and Loss statement. The reason why this won't work for Retained Earnings, is because the Retained Earnings account is a rollover of all previous fiscal years' net profit (or loss), and ClearBooks automatically swaps funds from the net income or loss into the account and doesn't record any visible transactions for it.
it is not as easy as a trial balance where you cr and dr from two nominal accounts.. it is different.