During Dvaya mantra initiation, adiyen was instructed to say ‘um’ instead of pranavam. In that case how to recite Vishnu Sahasranam as it contains pranavam in many places?

Scriptures have instructed that women should not chant pranavam when it appears in a mantra.
In Sahasranama, pranavam does not appear in any of the thousand names but it is included in the recitation at some places; so, it is not a compulsion that it should be chanted along with the nama and can be omitted.