@Ucboy4 - There are few ways to do it. You may create column or measure to get matched items using RELATED function, LOOKUPVALUE function, or FIRSTNONBLANK function .
Column1=RELATED（[one side field of relationship]）
Column1= LOOKUPVALUE(tableA[goal field], tableA[linked field], tableB[linked field]))
Column1= CALCULATE (FIRSTNONBLANK ( tableA[goal field], 1 ),FILTER ( ALLSELECTED( tableA), tableA[linked field] = tableB[linked field] ))
Once you look up the value from the foreign table. You can the use IF statement to check whether it is blank or non-blank. ANd, if it is blank, then get value from Primary table column. Example below:
Var ForeignValue = LOOKUPVALUE(tableA[goal field], tableA[linked field], tableB[linked field]))
If (Isblank(ForeignValue), PrimaryTable[Column], ForeignValue)
Hope this helps ! If you need mroe help, please share the screenshots of the tables or upload a sample .pbix file through one drive. Happy to help.
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Thank you very much !