i dont know where/how i can do this.

What do you mean "You don't know how to do this?" In the form designer, in the property sheet, under the data tab, set the grid's RecordSourceType to 1-Alias and its RecordSource to csrMstr.

Now, on the layout tab, set its ColumnCount to something other than -1. If you have the MSTR table open in the DE, you can use its fields as the ColtrolSources for the grid's columns and then edit the Columns ControlSources to say csrMstr.SomeField instead of Mstr.SomeField.

i get error message(alias name is already in use)

On which line of code?