There is no easy way to retrieve something deleted – you will have to go to the audit log (gear icon on top right of screen, ‘Audit Log’ option under ‘Tools’ category) to look for when you performed the action of deleting.
There will be a ‘View’ option to look at the last details of the transactions you deleted. However, you will be unable to restore any deleted transactions nor search them, and will have to key in a new transaction if you deleted any by accident. It is recommended to void rather than to delete any transactions, as voided transactions remain in the system and can be searched, retrieved, and amended, but will not affect your numbers in any way.