There isn't a way to do from the picolog software.
But if you create a settings file and then edit it, you can reorder the channels.
1. Save a settings file- (file menu - save as - set to pls file type).
2. Close picolog and open the pls text file.
3. If you search for '[Parameter' and look at the channel label on 3rd line below and then just re-number the '[Parameter' number to line you want it to be on.
ie [Parameter 1] channel will be on line 1, change to [Parameter 4] this will now be on line 4.
4. After saving close this file you will need to create a new data file. file menu - new data - save new plw file.