I understand that everything in shapr is based on sketches.
When I find out that one of the first sketches I used to build the part was flawed - like I should’ve put 12mm instead of 10mm - how do I go back to that sketch, change the dimension and then redo the whole thing?
Shapr3D is not a parametric modeler, it’s a direct modeler, so there’s no way to change a sketch and have it automagically update the solid made from a sketch. You either have to modify the solid directly or delete it and regenerate it with the updated sketch.
It’s best to thing of sketches as just that sketches or construction lines to help you construct your model. Once the model is built, forget about the sketches, adjust the model till it’s how you need it and use the 2D drawing feature to generate dimensioned drawings that will update if you change the model. Before they added the 2D drawings, grasping that concept was much harder.