As you want to merge these adjacent cells in "all 480 rows in the document," you could 'merge' the content of each pair of cells into a third cell in a new column.
Then select the third column, Copy, and with the column still selected, go Edit > Paste formula Results.
With the merge (actually 'concatenate') formulas now replaced with their fixed results, you can delete the two original columns, leaving the 'merged' cells of the third column.
Either of these formulas will do the job, They assume the first row containing data is row 2, and the columns are column B an column C.
Select any cell in column C. Press option-right arrow to insert a new column D to the right of column C.
Enter either of the formulas below into D2, then fill down.
D2: =B2&" "&C2
OR
D2: =CONCATENATE(B2," ",C2)
Place whatever text you want to separate the contents of the two cells between the quotation marks. I've used a single space.
Easiest way to 'fill down: Enter and the formula. Confirm it and close the Formula editor by clicking the green checkmark.
With the cell still selected, press command-D to copy.
With the cell still selected. scroll to the last row of the table, Press and hold command then click on the last cell in column D to expand the selection to the whole collumn (except the Header row).
Release the command key, then press command-V to paste the formula into all cells of column D (except the unselected header cell).
Confirm that column D contains what you want.
Edit the header cell manually to contain the label you want.
Click the column reference tab for column B, then shift-click (or command-click) the reference tab for column C to add it to the selection.
Place the pointer near th right end of either of the selected reference tabs, and click the v that appears to open the contextual menu. Choose Delete selected columns to delete the original columns B and C.
Regards,
Barry