To get a date in ISO format, use the following format string: yyyy-MM-dd'T'HH:mm:ss'Z' in the "Date Format" app.
If you are working with the Datastore, there is an introduction to it here. There are gotchas here.
When using a regex in the "Find and Replace" playbook app, you can use $1, $2, etc. in the replace value to insert matched groups. For example, if you find the regex (\S)\.(\S), this will find a non-whitespace character, followed by a period, followed by a non-whitespace character. Let's say you wanted replace the period with [.] (perhaps you are defanging indicators). To do this, you can use $1[.]$2 as the replace value. The $1 will be replaced with the non-whitespace character before the period and $2 will be replaced with the non-whitespace character after the period.