Once your search is applied within the Batch tool, select either Relate to Projects or UnRelate from Projects (1) on the left hand side.
NOTE: When using the Batch Operations Tool, always apply your search first and review the search results before progressing.
In this example, we are relating all of the search results to a new Project based on their address.
Next, select the Project (2) you wish to relate the Records to.
After finalising the changes you are making to the Records, click Execute (4).