Simple answer - you don't.
If the two units were the same model then you most probably could but because they are different models and series with different firmware then you can't.
What you should do is install the disks and format them then restore your data from your latest tested backup. From what you ask I assume that you don't have a backup of your data in which case it is going to cost you to recover that data. Assuming you use windows then you need to purchase some software that will recognise the linux file system on the disks and also sort out the JBOD formatting. Such software is R-Studio and while we do not endorse it I have downloaded the user manual and it appears to do what they say it will (we don't use windows and so can't test it). Download the manual from their site, read it and hopefully you will be able to recover your data if you decide to go down that path.
Good luck.