A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Simple Mid formula will do it for you:
Copy paste the below formula in the column next to xxxx:xxxx:xxxx. You might need to replace A1 with the right cell reference in your worksheet.
=MID(A1,1,2)&":"&MID(A1,3,2)&":"&MID(A1,6,2)&":"&MID(A1,8,2)&":"&MID(A1,11,2)&":"&MID(A1,13,2)