Find a variable string in a text file, modify it and replace it.

Hi,

I'm working on a script to merge txt files on a csv file.
My csv file is generated with autoit like this :

FIRSTNAME Lastname;BAT. T;225;XXX 034 458;50XXXXX;Dell Optiplex 790...
FIRSTNAME Lastname;BAT. T;225;XXX 034 458;50XXXXX;Dell Optiplex 790...
FIRSTNAME Lastname;BAT. T;225;XXX 034 458;50XXXXX;Dell Optiplex 790...
FIRSTNAME Lastname;BAT. T;225;XXX 034 458;50XXXXX;Dell Optiplex 790...
etc...

Each line data is different but the general formatting is the same (Name;Localisation;Room;Computer;Serial;Model)

The computer name is always like this : ABC 012 345

Is there a way to remove spaces in each computer name of the file ? From ABC 012 345 to ABC012345 ?
Each computer name always start with GRE. Maybe by searching string like ";GRE ".
But I don't know how to do.

Thanks for your help.
Regards.