Turn back. The grammatical form is peculiar (literally, be made to turn back). If the punctuation is not an oversight the object is to suggest the compulsiveness of the change of route of the Dedanites.
Dwell deep; i.e. tarry in the deepest recesses ye can find, so as to avoid the calamities of the Edomites. The Dedanites, it will be remembered, were a tribe devoted to commerce (see on Jeremiah 25:23).
Isaiah had already, on an earlier occasion, given the same advice as Jeremiah, viz. to leave the beaten track and take refuge in a less exposed part of the desert, where shrubs and thorn bushes ("the forest," or rather, "the thickets") would secure them to some extent from observation (Isaiah 21:13).
See, however, verse 10.