how to turn of 5GHX radio on the Orbi router

> The manufacturer told me they will not work on 5ghz freqency [...]

   Ok, but that does not imply that a 5GHz signal from your router will
cause trouble.

> [...] and in order to set them up my phone automatically selects 5ghz
> and there is no other way to connect them so I need to be able to turn
> it off until I can connect then then I can turn it back on

   I now know nothing about even more things, including: what your "some
in home automation devices" are, who made them ("The manufacturer"),
what your "my phone" is, how you're supposed to persuade these gizmos to
connect to your wireless network using your "my phone", and, most of
all, how a 5GHz signal will cause trouble when you try to use a 2.4GHz
gizmo.

   As I said, I have a bunch of 2.4GHz-only Internet-of-Junk devices,
and the 5GHz signal from my router has never stopped me from configuring
them or from using them, once configured.  But, with no actual
information on any of your stuff, there's not much specific info I can
provide on any of it.

   I took a quick look at the User Manual for an RBR50, and didn't see
the control which appears on many other (non-ORBI) Netgear routers,
namely: ADVANCED > Advanced Setup > Wireless Settings : [ ] Enable
Wireless Router Radio (one for "(2.4GHz b/g/n)", one for "(5GHz
a/n/ac)").  So, I don't know how to disable your 5GHz radio.  I also
don't see why you would need to, any more that you'd need to shut down
all the FM radio stations in your neighborhood when you wanted to tune
in an AM/MW station.

   My advice would be to run the experiment, and follow the standard
gizmo-configuration procedure (wherever that might be written down), and
see what, if anything, actually goes wrong.  The only problem I can
imagine with that would be if your phone needs to talk directly to the
gizmo itself (which is done in one of the common gizmo-configuration
schemes), _and_ if your "my phone" is actually unable to communicate
with a 2.4GHz wireless access point.  (And, if that were true, then
switching off the only 5GHz radio around would seem to be an even worse
idea.)