I had made heart- shaped object. It had unparallel position which make me a little uncomfortable, so I want to change it. Btw, the object is like this

(Nodes that has been marked by blue colour is what i want to make it parallels)

Can i put them into parallel position? Is it possible?

The Align dialog (Ctrl+Shift+A) has node alignment widgets.

If symmetry is desired, another useful workflow is to use the Mirror path effect, so only one half of the design needs to be created and the other half is automatic.

Hey... It's working

I tried your recommendation of Node Alignment widgets first and it can be parallelized. Also, I try the Mirror path effect and here is the result of them both. Thank you for the recommendation