You can't. Licenses are for the hard drive (or NAND storage soldered to a RouterBOARD). If the storage changes the license becomes invalid. Converting the image to a different format changes the virtual hard drive, so the license becomes invalid. You cannot work around that.
You can try to email firstname.lastname@example.org
to get official help. Other users cannot help you with this.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.