Where is String Builder action in Nintex WF O365 ?

I tried searching in the site to find string builder action in O365. Does anyone happen to use this favorite on-prem nintex functionality in O365 ? if yes what is the name of it or work around ?

I am working on a project to build assessment for migrating on-prem site with bunch of Nintex workflows to O365 and currently running a trial version of SharePoint enterprise. I request community members who already involved in such efforts to guide me a bit here.

Thanks.