You need to add server to farm in sharepoint, then follow the stp by step below. Let’s say, there is some issue due to which you disconnected web front-end server from sharepoint farm. Once issue resolved, you need to join web front-end server to farm again.
By time workflow content grow high which will impact performance. So as to improve performance of workflow for sharepoint site containing nintex workflow, we can move nintex database from default all in one content to a dedicated nintex database. Moving nintex database to dedicated content database from common db is called split database.