házmelo saber

Let me know.

Hazmelo saber" - Make it so it is known to me. As you might know, haz is the second person singular of the imperative of hacer ( to make),

thus, me (házme,) turns the verb into a reflexibe imperative,

which brings the action back to the speaker,

the pronoun lo just replaces whatever is being made,

and then whichever infinitive verb you add after ( in this case saber) just adds meaning.

Házmelo" could have a sexual connotation also

Do it to me.

Alternatively we can say “Me avisas”, “Infórmame”, “Me dices…”