Thorsten Klein , No screws, this is really not a repair for the inexperienced because the Sim-Card reader for your device is soldered to the mother board and the heat generated could cause further damage if not very careful. If you do want to give it a shot, I will post a link to a tear down guide to get you inside the tablet to check the Sim-Card reader and will also post a link showing what is involved in changing a Sim-Card reader attached to the board (not your exact model but gives you an idea). If not up to doing repair pop into a good local cell/computer repair shop and have them take a look and estimate repair. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.
[guide|30687]
https://www.youtube.com/watch?v=3fw-gf9to9I