You can use below query to check inside DB whether the Deletion Service is running regularly. If it's running, then leave it to Deletion Service as it will have these POA records deleted.
USE MSCRM_CONFIG
select * from ScaleGroupOrganizationMaintenanceJobs where OperationType = 14
Besides, you can also use below script to check out inside the POA table to confirm how many records having 0 for both fields (accessrightsmask and inheritedaccessrightsmask). You can delete these records manually, so just leave it to Deletion Service to have them deleted (usually, these records will stay there for 90 days, and then Deletion Service will remove them).
select objecttypecode,accessrightsmask,inheritedaccessrightsmask,count(*) as Total
from PrincipalObjectAccess with (nolock)
group by objecttypecode,accessrightsmask,inheritedaccessrightsmask
order by total desc
