You can use
Flatten To String Function to divide 64-bit floating-point data into 8 pieces of 8-bit data,
while you can use
Unflatten From String Function to combine 8 pieces of 8-bit data as shown below.
Note: This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project.
To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW block.