Where does “ím” come from?

ím (Proto-Indo-European) comes from Proto-Indo-European éy, from Proto-Indo-European h₁e-.

Ancestry of “ím”, step by step

Step	Language	Word	Meaning
1	Proto-Indo-European	éy	the; demonstrative pronoun; this one, he
2	Proto-Indo-European	h₁e-	—

ím — Etymology, Origin & Word History | Etymology Explorer