I have a lookup function on one worksheet, that will check if the number I
input exists in a named range (accruals) on another sheet named Accruals.
What I want to do is say.

If this number exists then find the cell reference it appears in, in
worksheet Accruals and change the amount under column amount to zero.
These numbers are not sorted but are unique

Po SHeet
PO supplier date amount

Accruals columns - Accruals sheet
Po, supplier date, amount