Specify the default symbols for groups in graphs

File > Options > Graphics > Data View With Groups > Symbol Types

For graphs that have symbols, each group is represented by a different symbol. Specify the default number and types of symbols that are available. The changes you make to the defaults remain until you change them again, even after you exit Minitab.

If the number of groups in the data is higher than the number of available symbol types, then Minitab repeats the symbol types.