Multiple lookup SPD Workflow: How to filter list item based on two columns in SharePoint designer 2013 workflow?

In SharePoint designer you can lookup only one column.

So, create a calculated column in the source list and concatenate the two columns.

Calculated column (KEY) = CONCATENATE([ColumnA],[ColumnB])

Now you can perform lookup on this calculated column.

In SharePoint designer create a variable by concatenating the columns containing the data same as ColumnA and ColumnB.

As SPD doesn't have concatenate function so, you can use string builder to achieve the merged string: