This is quite hard. You could insert "act on", "pay heed to", "yield to". There are some phrases you could use too. It's normal to talk of "preconceptions" in the plural or of a specific preconception. I am not sure that this is a good sentence to give to learners - where did you get it from?

There are many things you could "do" with preconception; in this case they want to say you must not "do" anything "positive", so: Synonyms of 'pay attention to' We must not [pay attention to/listen to/heed/respect] our preconception. Synonyms of 'think of' We must not [think of/consider/regard/mind] our preconception. Synonyms of 'use' We must not [use/rely on/practice/employ/react to/consider] our preconception. Synonyms of 'value' We must not [value/nurture/cultivate/embrace] our preconception.