Follow below steps:
1. Select required Dimensions/Measures.
2. Now create a calculated field to calculate the index as
Index = INDEX() .
3. Now create another calculated field to group all rows by even and odd row numbers.
group = IIF([Index] %2 =0,0,[Index])
4. Now convert the field into discrete and drop the group filter in filter shelf and unselect zero from selections to show alternate rows from beginning for all rows.
Hope this helps you.