If you are employed in an organisation with very few employees, this might be difficult to arrange. In such circumstances, it might be possible to gain your employer's agreement to enlist the help of someone external.
In larger employing organisations, it should be possible to agree with your employer for your grievance to be heard by an independent manager. This would particularly be preferable where your grievance is against your immediate manager.
Consult your organisation's grievance procedure to see if any provisions are made for this situation.