Without the assistance of third-party apps, you can recover boot partitions by making changes to the Boot Configuration Data (BCD) using Windows Command Prompt. Here's how:
Boot your PC with the Windows installation media.
Launch “Command Prompt” (Windows + R > cmd).
Enter bootrec /fixmbr and hit Enter.
Now, enter bootrec /fixboot and select Enter.
Proceed to type bootrec /rebuildbcd and hit Enter.
Finally, reboot your PC to recover the deleted partition.
You can also recover boot partitions in Windows 10 by simply re-installing the Windows OS. Before proceeding, ensure that you have backed up all your files to prevent data loss.