Hi Mohisinali,
Thanks for reaching out to microsoft Q&A.
There is a resolved answer I found to your question which has been earlier asked by other user. Please see if this helps.
https://www.unixarena.com/2019/12/azure-how-to-convert-disk-from-premium-to-standard-ssd-vice-versa.html/
https://learn.microsoft.com/en-us/azure/virtual-machines/windows/convert-disk-storage
Please Upvote and Accept as answer if the reply was helpful.