I have found out how to change the PARTUUID from this link :-
I used fdisk.
After changing the PARTUUID with fdisk I changed PARTUUID in cmdline.txt and also in /etc/fstab to the new PARTUUID after doing this the USB drive booted with the new PARTUUID
Some of the things which confused me before finding out how to change the PARTUUID using the supplied link.
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To change the PARTUUID you change the disk identifier with fdisk
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The PARTUUID (disk identifier) is changed by working on sdx NOT sdx1 or sdx2
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After completing this procedure both partitions on the Dietpi USB drive will have PARTUUID’S similar to PARTUUID=64123f76-01 and PARTUUID=64123f76-02