GB Ordnance Survey Map reference for InReach Explorer+

Great Britain Ordnance survey map references have disappeared from my InReach Explorer+.  I used to get GBOS datum on the units settings along with a load of other world-wide datums, but now all I see are NAD27 ConUS, NAD83, and WGS84.  All our maps in the UK show only OS references, so the location info now appears useless.  Any advice welcome.