Nearly everything you would ever need to know about this printer can be found on the unofficial MP Select Mini Wiki. As of this writing their SSL cert had expired so you may get a warning about that.
There are also things you can download from there and I want to be clear that you do so at your own risk. I have nothing to do with this site and can not guarantee that any executables you may find on the website are safe.
This printer was a clone of the Wanhao Duplicator i3 Mini.
Other clones exist as well.
BE EXTREMELY CAREFUL.
I definitely give absolutely NO guarantees on this. I built up a custom firmware based on numerous other people's work and I put it up on github. These printers came with two different micro controllers and the ones that used the STM32F103 chips were not necessarily common so it took a lot of extra work to get this going.
You can find my github fork of Marlin here at Marlin For MPSMv2 On MCU STM32F103.
Importantly I added this readme to the repo with all of the info I knew at the time. README For My Marlin Fork
I can try to answer any questions you have but updating the firmware with custom firmware is not for the faint of heart and you could easily brick your printer and make it a nice paper weight. If you decide to go down this route any fallout is on you.