Ignoring the Windows/batch stuff it sounds like you're trying to change
the value of an environment variable by changing it's value in the
ENVIRON[] array within awk. You simply can't do that. ENVIRON contains a
COPY of the environment variables names and associated values when awk
starts up, that's all.

Look (in UNIX, no idea what the Windows equivalent is):

$ x=7; awk 'BEGIN{ ENVIRON["x"]=8; print ENVIRON["x"] }'; echo "$x"      
8
7

If you want to change the value of a variable in your environment as a
result of executing an awk script then you need to have awk return that
value and populate your variable from it, e.g.

$ x=7; x=$(awk 'BEGIN{ ENVIRON["x"]=8; print ENVIRON["x"] }'); echo "$x"
8

or generate a script to set the value and execute that script, e.g. with
UNIX eval:

$ x=7; eval $(awk 'BEGIN{ ENVIRON["x"]=8; print "x="ENVIRON["x"] }'); echo
"$x"
8

Regards,

   Ed.