If the window installation is also a new construction, contact the installer and get them back to install it properly.
Tell them that it is unacceptable in this condition. Also if you haven’t already done so, don’t pay them as maybe this will guarantee that they will come back. If they don't then at least they haven't been paid for their poor work
If they won’t help and they sub-contracted the work from a builder etc contact the builder about the problem.
Don’t let them get away with shoddy workmanship!
Just my $0.02
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