From your description, it seems you are trying to convert the first four rows into column values and then merge them with the rest of the data. You would like to use the following dataflow transformations:
Filter: Use a Filter transformation to separate the first 4 rows which are intended to be column headers from the actual data.
Transpose: Use Transpose transformation to rotate the selected rows into columns.
Top N: Use Top N transformation to select the top record after transposing as it would be your final header row.
Rename Columns: Use Rename Columns transformation to replace existing column names with new ones based on the transposed header row.
Filter: Use another Filter transformation to get the rest of the data excluding the first 4 rows.
Join: Perform a Join operation to combine the header row with the remaining data.
Please note that Dataflow transformations in Microsoft Fabric might not directly support such complex transformations. If you have access to Spark or Python, these types of transformations can be more straightforwardly implemented using those tools.