I need help using Match, Index, and ArrayFormula.

I need any text inputted in a column to make the adjacent row be populated with the corresponding number on a different sheet; however, if the same text appears in the column, it must correspond to the same number. I need it to look like this:

Sheet1:

A1
123
1234
12345
123456

Sheet 2:
A1 B1
sam 123
todd 1234
bob 12345
sam 123

But instead it looks like this, using this this formula: =ArrayFormula(INDEX(Sheet1!A1:A28, MATCH(A1:A30, A1:A30,0))):

Sheet 2:

A1 B1
sam 123
todd 1234
bob 12345
sam 123456

Put this formula in Sheet1 B1
=IFERROR(INDEX(Sheet2!$A:$A,MATCH(A1,Sheet2!$B:$B,0)),"")

I'm not sure if I explained correctly:

I need the A column on sheet 1 (the numbers) to appear in the B column on sheet 2 with the condition that the repeating text in column A on sheet 2 corresponds to the same number from column A on sheet 1 each time. I want to paste the formula into the B column on sheet 2. Thank you for your help so far.

If I understood

In Sheet2!B1 use

=Sheet1!A1