which software can help me?

I have a scanned model of a miniature seat cushion, I would like to use exactflat to flatten the 3D models into 2D patterns, but before that, i need to create different pieces on the .stl file.

for example, the seats are made of different face and pieces, which need to be define before exactflat can allow me to choose the pieces to flatten.

I think spiline function would be suitable for this i am looking for, but which software is best for this?

in the attachment is a headrest, which i need to split themand define the different pieces beofer letting exactflat flatten it.