The Manage Expenses feature is in the Bank Transactions tab in the QuickBooks Solopreneur app.
Navigate to the Bank Transaction tab and tap the three-dot icon at the upper right corner. Select Add Transactions, and choose the Expense option under the Type tab.
If the Expense option is still missing, you can log in to your QuickBooks Solopreneur account via a mobile browser as a workaround to manage your expenses.
Just click the Reply button below if you have other concerns.