It is not possible to have two separate managers who are in different posts managing an employee who only has one job role.
SelectHR works on either a post to post or person to person basis (depending on your configuration, but typically post to post is used):
Post to Post - Employees in Post A manage Employees in Post B
Person to Person - Employee A manages Employee B
When using post to post reporting, as you can only assign one managing post to a post record, it is not possible to have two different managers who exist in two different posts managing a single post.
However, it is possible to have two managers in the same Post managing an employee.
When using person to person reporting, you can only assign one manager at a time. It is not possible to specify multiple managers with basic system functionality.
If the employee has multiple active appointment records, then you can specify a manager for each appointment separately, but this should only be done where an employee genuinely has multiple roles in your organisation.
It may be possible to have a bespoke solution implemented on your system to allow more than one manager to be assigned to a post or appointment record.
If you are interested in seeking a bespoke solution, please reach out to your account manager, who can assist you with getting this raised as a request.