Copy the initrd to somewhere else, say /tmp:
mv initrd.img to initrd.gz
*the mv to .gz is needed otherwise gunzip won't work/it will refuse to operate without the correct .gz extension
gunzip initrd.gz
cat initrd | cpio -idmv
The last command extracts the contents of initrd to your present working directory.
For 7z .lz initrd
mkdir initrdextract && cd initrdextract && cp initrd.lz initrdextract
7z e -so initrd.lz | cpio -id
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