DIY C-41 the same as 35mm.

My personal results with old 126 benefited with additional 30 seconds in the color developer. The negatives still were off balance and slightly fogged but scanned well enough.

Some people like to develop old film at colder temperatures for longer times. I have not tried that with C-41.

Cut the cartridge open carefully for reuse. There is color 35mm non-perforated film available for those who enjoy reloading their 126 cameras.