just a quick question. We have a requirement where we need to send email to assigned user if task is selected 'open'. Now I have tried this in process builder and flow, so far it's working. what i want to know though is if it's possible to apply this all past Task records that has still a status of 'open'? thanks
So, there are a couple of approaches here:
Write a Scheduled Flow that queries for all the past Tasks and then invokes the same flow used by your Process Builder to send the emails. The scheduled flow would be defined to execute once.
Initiate some DML action (such as via Data Loader) on all past Task objects that are still Open such that the Process Builder triggering condition executes and the decision block that starts the email actions becomes true. Note that based on how you defined your PB and Decision Block, you may not be able to do this (as the decision block's satisfying conditions may be based on changes in fields that your Data Loader action wouldn't be altering, or, the Process Builder is set up to run on Create only). Sometimes you have to toggle a field from one value and then back to its original value in order to get the PB conditions to execute -- that is, two Data Loader runs)