Hi,

You can check whether the logged in user is in particular group or not like this,

self.env.user.has_group('hr.group_hr_manager')

Where, hr.group_hr_manager , is the external id of the corresponding group.

Code sample:

def action_set_present(self):
    if not self.env.user.has_group('hr.group_hr_manager'):
        raise UserError(_("You don't have the right to do this. Please contact an Administrator."))
    self.write({'manually_set_present': True})

Thanks

Using has_group can check user is related to particular group
Example default hr core module code 

@api.multi
def _compute_show_leaves(self):
    show_leaves = self.env['res.users'].has_group('hr_holidays.group_hr_holidays_user')
    for employee in self:
        if show_leaves or employee.user_id == self.env.user:
            employee.show_leaves = True
        else:
            employee.show_leaves = False