The first question is. Can you check your bag through or not. This will be important and affect your transit in Frankfurt.

Case 1: You can not check your bags through:
1) You arrive with Condor in Terminal 1
2) You will go through immigration
3) You have to pick up your checked luggage
4) You will go through customs and exit the secure area
5) You have to check in your bags with Tunis Air (Terminal 1, Area C) and get your boarding pass
7) You have to go through passport control for leaving Europe (Schengen Area)
8) You have to go through security

My guess is you should consider at least 2hours for this including you are a slow walker. Maybe you can arrange for some kind of assistance. I think the airport offers such a service

Case 2: You can check your bags through
1) You arrive with Condor in Terminal 1
2) You follow the sign to the depature gate of your Tunis Air flight. If you don't have a boarding pass you might have to leave the secure area and go to the Tunis Air Check-In to get one. You might get one at the gate, too but not 100% sure. If you stayed within the secure zone you should be able to go directly to your gate, you might have to go through security again

Transfer Guide Frankfurt

Rankfurt Airport Website

You might should consider requesting Passenger Support Service. You have to this at least 48hours in advance by calling your travel gent or airlune