I am unsure about your intend to remove leading `_` this might lead to `chown: _user not found` when `chown`ing

try

    awk -F: '/^#/ { next } {printf "chown %s \"%s\"\n",$1,$6} ' my_etc_passwd

where

 - `-F:` tell awk to use `:` as separator
 - `/^#/ { next }` skip line starting with `#`
 - likewise add `/^_/ { next }` to skip line starting with `_` (if need be)
 - next pattern/action print chown command.

If result look OK, just pipe to `bash`