Description
You can reset the IP address of your S7-1200 PLC using the function Reset to factory settings of the STEP 7 Basic software.

Reset IP

1. Launch STEP 7 Basic and open the project containing the S7-1200 PLC you want to reset.
2. In the project tree browse for the S7-1200 PLC and highlight it.
3. Click the toolbar command Go online. The title bar changes to orange. You have online access to the S7-1200 PLC now.
   
   
   Figure 01
    
4. Double click item Online & Diagnose in the PLC folder in the project tree. The Online access dialog window of your PLC opens.
5. In the Navigation area browse for  functions > Reset to factory settings.
6. Select  radio button Reset IP address in the work area and click Reset button.
   
   
   Figure 02
    
7. A Reset to factory settings dialog box opens. Click the OK button.

The IP address will be erased.

Note
Check on the IP addresses of the PLCs used by clicking menu command "Online > Accessible devices...".