Lindahem was in Apol's juristiction and must have been near Lindeoorden - near/in the Linde Wood/Forest. Near Stavris/Staveren and in the area of Flyland.
It was vanished it said, under the sea, so why are you looking for it????
Edited an error I made and to add this, the mention of the vanishment of Lindahem isn't the only mention of it...
--Apol, Adela’s husband; three times a sea-king; Grevetman of Ostflyland and Lindaoorden. The towns Liudgarda, Lindahem, and Stavia are under his care.
Oh really? "Under the sea"? No, it says it was never found again.
Same thing with that 'Lindashem' in Germany..it vanished. But it didn't, it was just a legend.