Natasa,
If you don't already have one, set up a table for User Groups. Make the key field be the user and have a dropdown (text - multiple choice) field with the various groups (can be a parent table or just a pre-defined list in a field). Now in your Assignments table, create a Formula - User field called Current User with the formula just being User(). This will pull the current user value for whoever is logged in. Now you can do a lookup from your User Groups table to pull the user's assigned group down to the Assignments table as a Current User Group field. Use this field to compare against the Assignee Group field for your report filtering.
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Oana Toma
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