As this is single-node, so it will be disruptive.
Looks like the image is already downloaded on to the local node, as seen from system imaga package show command, hence we just need to point it to the location.
node::> system node image update -node node0 -package file://mroot/etc/software/image.tgz -setdefault true
Step 2: Oncce node is rebooted, and you are logged in:
cluster1::> system node image show -node node1
It should show 9.1P19 as 'default'.
In your case:
cluster3::> system node image update -node cluster3-01 -package file://mroot/etc/software/91P19_q_image.tgz -setdefault true
Just for info : Automated upgrade on a single-node cluster is supported beginning with ONTAP 9.2 (It is automated in terms of background tasks, however it is disruptive as well b'cos of only single-node)