Most refill kits come with instructions which will tell you what color goes in what hole.
That said, my advice would be
don't do it!
Refilling ink cartridges is always risky. The inks in those refill kits may or may not be correct for your particular printer.
The wrong ink can ruin a printer.
I have three Z-25 printers. I bought the first one because it was on sale for $34.95. I bought the second because it was cheaper than buying ink for the first one. I bought the third one for the same reason.
Somewhere along the line (and because, having three Z-25 printers, it didn't matter if I ruined one) I bought a refill kit. The instructions for the refill kit were quite explicit about where to put each color of ink, so there were no problems along that line. However, even after several attempts,
I was never able to get any of the three printers to print reliably with refilled cartridges. I now have three paperweights / doorstops, caused by my failure to take my own advice.