Excel: IFS or Nested If Statements

I'm having an issue writing an IFS statement in Excel.

This is what I would like to happen: User chooses from a list of 8 names in B1. Based on the selection of B1, in B2 the user will get a dropdown of a more refined list to choose from.

This is how I have the IFS statement written so far, which is causing trouble:

=IFS(B1="A",A),["B",B],["C",C],["D",D],["E",E],["F",F],["G",G],["H",H])

I have also written this which doesn't work either:

=IFS(B1="A",A),[B1="B",B],[B1="C",C],[B1="D",D],[B1="E",E],[B1="F",F],[B1="G",G],[B1="H",H])

I keep getting error messages.

Does anyone have any suggestions?

Thank you!