Can you please make this letter different to the wording of the PhD attestation letter? Also, are you already a Dr.? If you are already a doctor, you may want to consider adjusting the grammar. For example: I confirm that XXX has been working (better say: I confirm that XXX worked). As a Graduate Research Assistant, he assists me in research activities (better say: As a Graduate Research Assistant, he assisted me in research activities.
Finally, change the top and bottom parts of the letter. It looks exactly like the PhD attestation letter and it may confuse the Visa Officer at CIO.