Recover Fortiweb Admin password

You need atleast a prof_admin account/password to reset/recover the admin password.

https://docs.fortinet.com/document/fortiweb/7.4.0/administration-guide/180461/resetting-passwords

If you are running older version (I belive 5.x or below) the maintainer account can be used. Below document explains the procedure 

https://fortinetweb.s3.amazonaws.com/docs.fortinet.com/v2/attachments/0d8c9206-202e-11e9-b6f6-f8bc1258b856/fortiweb-v5.9.1-admin-guide.pdf 

I searched  a lot on this. The only option available is to reimage the device as said here - https://fortinetweb.s3.amazonaws.com/docs.fortinet.com/v2/attachments/2c7f658f-7d40-11ec-a0d0-fa163e15d75b/FortiWeb_7.0_Administration_Guide.pdf