You’ve not provided release details; nor specifics as to type of re-install (ie. clean? unclean etc), but I suggest exploring our testcases which include a description of an unclean install.
I was asked to write an answer over on askubuntu covering it, so I’ll provide a link to that too, pretty much the same detail however written with a different focus
https://askubuntu.com/questions/446102/how-to-reinstall-ubuntu-in-the-easiest-way/1451533#1451533
Those links talk about an unclean install, which is something I’ve always loved about Ubuntu… but a clean install is easier with calamares as you can just use the Replace partition option, or as always tell the installer what you want via Manual Partitioning.