I own a Volkspolizei Brno 98 (tgf1950) which had the same issue. As I recall, I used the following procedure. Used old 6" Pozidrive screwdriver, with damaged head reground for use as drift punch, to depress catch and tapped the floorplate to the rear, using a 20oz hammer and and a suitable piece of steel. The floorplate was very tight, necessitating careful work with a second cut file to relieve high spots but the situation was exarcerbated by loose propellant left in the action by the previous owner.
I also used penetrating oil. A little bit of Kroil left to soak in over 24 hours would be a very good idea. Don't waste your time with CRC 5.56 or similar.
Good luck.