Problem with Rename column titel

My basic file read in with Excel Reader node has various columns. Including columns that start with a 7-digit number, of which the first 3 digits always start with 605. After the 7 digits, there is a longer alphanumeric sequence separated by spaces. My goal is to create a workflow that automatically selects the columns starting with 605 and renames the column title to the first 7 digits, i.e. 605xxxx. This means that the alphanumeric sequence attached to the original name should no longer be displayed. I’ve already used the String Manupulation Node and the Coumn Rename Node for this, but I didn’t get anywhere with both. I think that one difficulty is, among other things, that the content contains multiple lines in the string formated cell - example:

6052311

KA3

0M41

R 1300 R

I just want 6052311 in the title column. I’m asking for urgent help.