I have query w.r.t to re-running process models which have halted due to errors.

It sounds like what you're after is the Edit Process mode: forum.appian.com/.../Edit_Process.html

You can access it by selecting Edit Process in the dropdown in the top-right corner of the Process Modeler when you are looking at the process instance you want to edit.

@george, Added to above, you can use the Shared Component namely - IFM Manager - where in it can deal with such kind of instances in bulk. Please have a look into the Instructions document attached to this shared component:
https://forum.appian.com/suite/tempo/records/type/components/item/i8BCLGOdlMUpdGVqT-RV7oRg74uEGJO5CMZACzz_5W0L-UUHaRsMA-2Or_cSO-8rg/view/summary

IFM may be your solution here. However for some additional options, we have implemented this in a few different ways. One is using a combination of Set External Pvs (Process Upgrade plugin), to set the variables in the designated process, then call a Receive Message node in that process which runs a path to the script task again (attached). This is helpful for sub processes when you know the only waiting processes with errors are those with active Receive Message nodes (sub processes). We typically use this in processes with Query DB nodes set to continue on error and wait at a Receive Message node during this scenario. During DB outages we can have hundreds of errors - so they all wait at a Receive Message node and one call from an admin process resumes all instances at once, when we know the DB is back online (attachment #2).

Another method is with the Start All Nodes service of the Process Upgrade plugin. This would be used in combination with Set External Pvs as well, if you are not restarting ALL process of a certain pm!id, this will allow you to specify which instances to retry.

Process Upgrade: forum.appian.com/.../

Get and Set External Pvs: forum.appian.com/.../

Thank you