The answer to this question is highly dependent on if you are using LF Cloud or Self-Hosted. For the spirit of the answer I will provide both examples for anyone who finds this in the future

Self-Hosted - Main docs link

1. Navigate to the process in question and click the Access Rights tab of the left pane in the designer.
2. Here you can search for a group or individual user and click 'Add' to add them to the process. For your use case select Business Manager from the Role dropdown to give them the access they need. 
3. Test!

Note:

1. This also gives them access to run reports, shouldn't be an issue but important to know
2. Best practice is to use a group here as it makes it easier to allocate/deallocate users in this elevated position across many processes instead of needing to navigate to each process in question
   1. For example, a Clerk Manager group could be setup so any current and future processes involving the Clerks could use this group to provide all group users access to the Business Manager role

Cloud

The setup for this is a little more lengthy, but the overall goal is the same. I will speak to it at a high level and link documentation to provide the granular setup for this.

1. Create a team with the managers and designers needed to manage this process
   1. Similar to self hosted, but with more granularity, add the users/groups and configure their appropriate roles
2. Create a project for this team and name it appropriately
3. Inventory the necessary processes and their dependencies (forms/workflows/lookup rules)
   1. If workflows and lookup rules are shared across non-related forms processes opt to give the project access to global resources instead of pulling or  duplicating the shared resources
   2. find the forms processes from the Manage section from within Business Processes and click the "Migrate" button from the toolbar in the far right
      
   3. Migrate your processes to your project
4. Test!