Try changing the filter to 'Machine Type'. This will show you all the devices, one type at a time.
Select one of the device types, then check the box to the left of the 'Name' heading. You should then see that all the nodes have been selected, whether they are clickable or not, and the 'Assign dates' button should be enabled.
Click that and you'll then be taken to the assign dates page, where you can view the list of suggested dates, or assign your own if you have a custom device refresh policy which forces a replacement before the device is actually EoL'd by the vendor.
If you can't do the above, do what cvachovecj suggests and contact support