General ledger opening balances

I have to show opening balances in my trial balance. How do I do this?

Why ?
You could set the trial balance date the same as the opening balances date.

Brand new set of account from March 17. Have opening balance from last year to carry through

There is no need to start a new set of accounts for a new accounting period. Manager is a perpetual system. See this Guide: https://www.manager.io/guides/best-practices/accounting-periods.

A trial balance is a snap shot of a point in time, it doesn’t portray a movement in balances.

First time I’m using Manager previously used Pastel

If you are migrating an ongoing business to Manager from a previous accounting system, then you may need to set starting balances in various individual accounts. Some starting balances are set as you create (or edit default) accounts. Some are established as you create subaccounts, such as customers. Read the relevant guides for Customers, Suppliers, Cash Accounts, Inventory Items, Fixed Assets, etc. Then, if you have specific questions, please ask.

From what I have read in the tutorial, I am unable to create opening balances for expense and income accounts

That’s correct, you only have starting balances for Balance Sheet accounts and their sub-accounts.
Past income & expenses are reflect in the Retained Earning starting balance.