In Excel , merged cell will hold value only in the first cell and Excel then formats the view to show the cell value across other cells. Un-merge the cells and you will see the value retained in first cell only.
Hence when its imported to R or any other tool it will retain values in first cell while other cells will be empty or NA.
The easiest option for you to import the excel file as-is and use the "fill()" function from dplyr to fill down the values.
Pls view the help at "Fill function"