If you are trying to get it back to Skinny mode, you’ll need to use the method using a factory load file and DHCP.
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You will need to configure your DHCP server to offer configuration information on option 150. This is possible from the DHCP server that comes with FreePBX (you can set the option 150 address there). If you are using some other non-standard DHCP server, you will need to set it up so that it provides the phone with the correct TFTP server address.
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Once you have DHCP set up, you can use the Factory Reset Sequence to brick the phone. Note that there are several, depending on the specific model of the phone, so the one you are using may or may not work.
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In the TFTP server, set up the SEPxxxxxxxxxxxx.XML file so that the options (including the correct firmware version) is set correctly. Optionally (well, recommended but not required) is the OS79XX.TXT file (spelling and case are critical) which contains the firmware version for all of the phones supported by that file.
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You have to make sure that the firmware version file name is exactly the same as the firmware you are trying to load, and the load file names vary wildly from version to version.
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Once you get the SCCP firmware loaded, proceed with the instructions I reference in here:
Interesting new success with Chan-SCCP-B and SCCP-Manager (both from GitHub)
This will give you the full capabilities of the phone without having to patch anything. The Skinny module handles all of the heavy lifting.