This should be fairly simple to do with the “shrink wrap” method. – Or give retopo flow a try for more comfort.
If you are looking for a freeware automatic retoloplogy workflow, check out “meshmixer” and “instant meshes”. – Depending on what you want to do with the mesh, this might save some time. It is definetely a way to make the model 3d printable. If you need to create texture coordinates for it though, manual retopology would be better anyway to achieve clean edge loops to split along.
I gave it a quick try. Export from BfA to Meshmixer > Make Solid > Export to Instant Meshes > Retopology > and back to BfA in two minutes.^^
There is only a small damage at the bottom of the snailhouse, that should be fixed in the original mesh before the procedure.