Assume that your source table and target table is same and both database are in same sql server instance. If so then you add column with same data-type which you import from source table.
alter table add NewColumnName int null;
then need to update that table with update query with join
update TargetTable set
MyNewColumnName = T.SourceColumn
FROM SourceDatabase.schema.SourceTable AS T
inner join TargetTable ON TargetTable.PrimaryKey = T.PrimaryKey;
If your source and target database is in 2 differet sql server instance/network then you just need to create a link server to your target database and use that linkserver reference to the update query.