Complaints about the clerk's conduct from a cllr would normally be handled by the council itself, eg. its Staffing Committee, or a sub-committee panel created just for that purpose. Following that, the council, as the clerk's employer, would consider and implement the recommendations of the staffing committee (unless the committee was delegated authority to implement it themselves). That might include training, disciplinary, etc. They should perhaps seek advice before going ahead to make sure they comply with employment law, etc.
In practice, however, you may find the council is dominated by a group who see it as their job to protect the clerk at all costs. In which case, you might find your complaint is not deal with properly. Not much you can do if that happens.