to import a zfs pool already created is to type in the shell zpool import poolname.
if you still cant because it says used on another system you can then do zpool import -f poolname
so mine looked like zpool import -f Tank
this will likley still happen if you had to reinstall proxmox for me this last time io tried out trunas and didnt like that i couldnt use my os drive for some storage or there are more saftey nets in place.