Hi! Deleted emails can usually only be recovered within 30 days of deletion. To try this, open Outlook in a desktop browser view, go to the Deleted Items folder, and look for the option to recover items deleted from this folder. This recovery option is not normally available from the mobile app.
If it has been less than 30 days but the emails do not appear in Deleted Items, use the search bar and search for a word, subject, or sender from one of the missing emails, then make sure the search is set to All mailboxes. If nothing is found, the messages may have already been permanently removed and might no longer be recoverable.