You can change your accounting system at any time. Go to Settings > Connections. Disconnect your current accounting software, then connect the new one. Some things need care first:
Bank account and credit card accounts. If you switch from Xero or Wave to QuickBooks Online, select the bank account where Amazon pays you and the bank or credit card account for negative payouts. QuickBooks needs this to send invoices. Find them at Settings > Connections > Manage marketplace mappings: Payout bank account and Negative payout bank or credit card account.
Accounts and taxes. You will likely need to set up your accounts again. Taxomate must create the default accounts in the new software, unless you use your own. On Accounts and taxes, use Redo category setup, or open Quick Setup.
COGS and inventory. Cost of Goods Sold and Inventory accounts must be created again in the new software. Set them in the Accounts card on Settings > Inventory (Asset account and Expense account). Each account saves on its own.
You can also stay on QuickBooks and move to another QuickBooks company. Use Switch company in the QuickBooks row on Settings > Connections. If you reconnect and sign in to a different company than the one saved, the page shows Wrong account and names the saved company. Sign in to that company, or use Switch company. If Taxomate cannot reach QuickBooks, the QuickBooks page says Taxomate could not reach QuickBooks and offers Reconnect to your company. Switch company and Disconnect are then under Change or remove.
Reminder: Once your Accounts and taxes and settings are right, select Rebuild on every settlement that is not sent yet. Rebuild applies the new accounts and settings.