What are the steps for modifying a fitness tracker?

[webhead]

I received a cheap fitness tracker as a gift. As expected, the data it monitors is quite inaccurate. I was hoping to mod it into doing some funky stuff like install externals apps.
Anyone here who have attempted it- successfully or otherwise. Any leads would be helpful.
If nothing, any tips for 'cracking open the hood' and seeing how it works would be nice too.