unable to lookup a substring in a main string

hi all,

i have highlighted a particular scenario which i have to lookup.

please suggest.

when i lookup id='k002' against lookup table, i get output user='user-2'

but when i try to lookup id='k003' against the lookup table, i am gettign a blank output.

i am not sure when to add custom code to loookup a substring if present in a lookup table column , like in below scenario?

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