Solved remove partion zfs

I add more space to my 1st HDD from second HDD by using
zpool add mypool ada1p2 and my 1st HDD has increased the size

Now I want to take it back and leave as it is.
when I typed
gpart delete -i 2 ada1
then I got "gpart: Device busy"

but when I tried zpool remove zroot ada1p2
I got '
"cannot remove ada1p2: only inactive hot spares, cache, top-level, or log devices can be removed"

I also try this commad
root@bsdhome02:/usr # zpool create tank ada1p2
invalid vdev specification
use '-f' to override the following errors:
/dev/ada1p2 is part of active pool 'zroot'
I was thinking to force "ada1p2" to move out to "tank" pool

Thanks in advance
Once it's been added to the pool you cannot remove it. You will have to destroy the whole pool and rebuild from scratch.