Related List

[shubhi211]

Create a related list in INC form which will store the value of past Caller details.

Detail explanation: there should be a Related List name "Store Past Caller" under that tab, there should be the Name and email of the caller whose name was earlier set.

Like Person X was there in Caller of INC form and then that name got changed to Person Y 

so under related list: Person X and his email should come

[OlaN]

Thank you for explaining in more detail.

So based on that I can give some pointers.

Related list is not really meant to be used like that. It can show related things to the form shown, and the values available.
If your caller changes on the form, the old value isn't saved on the record, making it nearly impossible to make a related list from, since you no longer have access to the old value.

If you still want to pursue this, then you will first need to figure out a way to store all the previous values of the caller, when the caller changes.

And if you are going down that lane, then you might as well set up a field that stores the name and email address of the previous callers when the caller changes.
This could be easily done with a business rule, or a Flow.

OOB you can see all the changes made since the caller field is audited, so there's that too.

[shubhi211]

Like Person X was there in Caller of INC form and then we save the form and then again we change the caller field to Person Y

so under related list: Person X and his email should come

this is not possible ? right

but I think there is one way: one-to-many relationship. But don't know how to use that.

[James Chun]

I guess you can create a m2m table between the [sys_user] and the [task] or [incident] table.

Then create a Business Rule on the Incident table to populate the M2M table whenever the caller field is changed.

Then add the m2m table as a related list.

[OlaN]

Possible, yes, but it seems like a big thing to implement just to get the previous values (which are also shown in the activity stream).
And I guess in most cases the caller is not switched, so then the list will be empty.

Like James suggested below, it could be done with a M2M table for example, but again, it's quite a bit of work for (in my opinion) little gain.