Frozen tables occurs when you open a drawing in "NO-VIEW" rep.
All you need to do is to open the drawing again with "ALL VIEWS" rep.
And there you go! Now you can do any operation on tables.
"No Views" can be helpful with very large assembly drawings. It allows you to make text edits to tables without having to open the full drawing.
To open a drawing and un-freeze the tables, I do this:
Open the drawing and select Open Representation
You wil then get a new window that will probably say "All Views" and "No Views"...at the bottom of this window will be a button that says Create New Drawing Rep. Hit that button.
A drawing rep tool window will then open up. There will be two tabs, Look at the Drawing Display tab. At the bottom is a setting for Table Preferences. It is probably set to Frozen, click Updating and hit OK. The final step is to Execute the new rep in the Drawing Rep window. Select the new Rep (probably REP0001 if you didn't select a name) and you should be good to edit the tables
It might be a good a feature, but you probably reached limits of the software and need to break your model into more sub-assemblies. I open a drawing and I don't get asked if I want the view to load the models too. Under tables tab, inside Rows & Columns there should be a toggle for freeze and unfreeze tables, no buts about it. PTC failed on this simple option. Again. Should not have to google how to operate this feature.