userform index match from another workbook

I am attempting to populate a textbox using an index match that references the adjacent label

the original function was

=IF(INDEX(DRIVERALL,MATCH(n4,DRIVERLIST,0),MATCH("HAZEXP",HEADER,0))="","",(INDEX(DRIVERALL,MATCH(n4,DRIVERLIST,0),MATCH("HAZEXP",HEADER,0))))

where a cell referenced the name in "N4"

but i now want to move it to a userform

how can i word vba to populate textbox1 from a text value in Label1
Any pointers appreciated