I'm not sure If I'm answering the correct question, but if you want to know the targets true bearing from north you have to add your own course and target bearing.
lets say your course is 045 and target's bearing is 330 from your bow.
45+330 = 375
And when the true bearing from north is over 360, you subract 360 from the value
45+330 = 375-360 = 15 This is the true bearing from north
Now you can draw a bearing from your sub at the nav map to bearing 15 from north.
This is the method I've been using when drawing an intercept course on the nav map
Hope this helps
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