You will need to carry out VSM (volume snap mirror) from the secondary FAS2020 to the primary FAS2040 then break the replication bring on line and then restore the snapshot.
dont forget to verify your snapmirror.allow or legacy options to allow VSM
I would go with something like:
FAS2040> vol create newvol aggr0 100g
FAS2040> vol restrict newvol
FAS2040> snapmirror initialize -S FAS2020:oldvol FAS2040:newvol
FAS2040> snapmirror status
once mirrored
FAS2040> snapmirror quiesce FAS2040:newvol
FAS2040> snapmirror break FAS2040:newvol
FAS2040>vol online newvol
FAS2040> snap list newvol
FAS2040> snap restore newvol neededsnap