Target system mapping in synch editor

I have a created a new synch project to sync data from target system to new custom table which I have created at One Identity side. I am using native database connector.

The expectation is I want to get data from two tables at the target into one Custom table  at the one Identity side. There is a column which is common in both the tables, but there is no foreign key existing.

Could you please suggest what are the possible ways to map the data.

Thanks in advance!