I don't think you need step 2 as you have already set partition type on Customer attribute for Process, Incident and Request, so make sure Customer attribute is still set for Customer partition type.
The additional step you need is to set the partition attribute on End User. In Administration select End User, User type and select the action Set Partitioning attribute. You can then set the partitioning attribute on the User i.e. 'Current Group' or 'Primary Group'. Then the partitioning knows that the Primary/Current Group on the Customer needs to match Customer on Process/Incident/Request.
Then Users will only see tickets which have Customer equal to the User Current Group (or Primary Group) as well as any tickets with blank Customer.
So, you will also need to ensure that when tickets are raised, the Customer attribute is set to the same as the Raise User Customer (Primary Group).
I hope this helps.
Thank you philw. If I understood correctly this will mean that specific End User will see all the tickets with same Customer as his Primary or Current group? I did the Set Partitioning attribute part and it is still not working. But also if this worked it will not do what I tried. I want End User to see ONLY tickets he logged and not all the tickets with same customer as his primary/current group. Currently in our system Customer attribute on Incidents/Requests is used like department, i.e. each Customer groupm has more end users. Any other suggestions?