How to select several values into variables in PLSQL

Your query returns a table of two columns and an unknown number of rows. Select these into a collection of a two-column record. Instead of a mere INTO you need BULK COLLECT INTO for this operation.

Once you are there, you can fill your separate variables in a loop:

DECLARE
  TYPE t_record IS RECORD (parameter VARCHAR2(100), value VARCHAR2(100));
  TYPE t_table IS TABLE OF t_record;
  v_table t_table;
BEGIN
  SELECT parameter, value
  BULK COLLECT INTO v_table
  FROM TABLE(my_db.workplan.get_pp_params(in_pa_nummer => 'NR04640992', in_par_typ => NULL));

  -- do something with that result, e.g.
  FOR i IN 1 .. v_table.COUNT LOOP 
    CASE v_table(i).parameter 
      WHEN 'Arbeitsanweisung'      THEN v_arbeitsanweisung    := v_table(i).value;
      WHEN 'Maschinengruppe'       THEN v_maschinengruppe     := v_table(i).value;
      WHEN 'Max. Anz. IC pro Tape' THEN v_max_anz_ic_pro_tape := v_table(i).value;
      ...
    END CASE;
  END LOOP;
END;

Another option: pivot your data to turn your rows into columns. With conditional aggregation:

BEGIN
  SELECT 
    MAX(CASE WHEN parameter = 'Arbeitsanweisung' THEN value END),
    MAX(CASE WHEN parameter = 'Maschinengruppe' THEN value END),
    MAX(CASE WHEN parameter = 'Max. Anz. IC pro Tape' THEN value END),
  INTO v_arbeitsanweisung
     , v_maschinengruppe
     , v_max_anz_ic_pro_tape
  FROM TABLE(my_db.workplan.get_pp_params(in_pa_nummer => 'NR04640992', in_par_typ => NULL));
END;