Hi Vandana,
"Change View" couldn't be enabled for lookup fields in Customer Journey Designer, it is by design.
In general, we could enable the "Change View" feature for lookup field by selecting multiple views in view selector.
e.g: By default, view selector is not enabled for Content Settings field of Customer Journey.


We could add multiple views to selector:


However, lookup fields in Customer Journey Designer are restricted to only one view, and the designer is not customizable.
Thus currently we couldn't change view for Marketing Email, Marketing Form etc. when building a customer journey.
Regards,
Clofly