If you can still login with another user that has admin privileges and can import LCM you should do the following.
1. Log into another environment (DEV, PROD, etc)
2. Make sure you know the password for the admin user on that environment and export the native users with LCM
3. Log into the environment where you forgot the admin user account and import the LCM you exported with native users
After you import the LCM native users the admin account should have the same password as the one in the other environment
The user would need at least the LCM administrator role, if the user was a Shared Services administrator they could log into Shared Services and change the admin password
If a user has the LCM administrator role then they can just export the users artifact, edit the users.csv file and change the password for the admin account, it will encrypt when it is imported back in.
There are other secret ways to do it though
Below is the way to reset password to its default.
Login to your database with the user/password that is the owner of the shared services repository.
Run the following SQL command in Oracle SQL Developer or equivalent tool user by your Relational Database System.
This will set it to default password which is password