You can reset the admin password using the RESET button on your Synology product. To reset the product, use the paper clip to gently press and hold the RESET button for about 4 seconds until you hear a click and then release the button immediately.

This does not format the Synology product, but restores the admin account's IP, DNS, and password to their default values and resets the guest account to the disabled state. The default password for the admin account is blank.