Condition Column to return value from different row

Dear Team,

I hope you're doing great! 

Could someone please help me with the following if statement I'd like to add to a conditional column in Power Query?

Unfortunately, PO value is given as  "#/#" in one column. However, the same value can be given from different row where the Document Text is identical to the case where PO is "#/#". Ideally, I'd like to exract the figure from the row where the Document Text is identical or duplicated and PO is e.g. 450000xxx and not '#/#"

1) PO.UP is #/#

2) However, Document Text is identical in another row in the same table

3) Whereas in the identical row has almost always a value in the so called PO Colum e.g. 45xxxxxxx

4) Ideally, I'd like to assign a new PO.UP2 colum to extract the value in step (3) 

Any ideas how to do this with Power Query?

Thanks a lot for the help