Hi Asmita,
Please contact Pearson VUE customer support for help with rescheduling:
https://home.pearsonvue.com/microsoft/contact
In addition to above, please ask your question in the Microsoft Certification forum using link below. There are support moderators over there that will respond to your question in 1 business day and can assist with fixing errors that may be preventing you from rescheduling:
https://trainingsupport.microsoft.com/en-us/newthread?threadtype=Questions&forum=mcp
Please click Accept Answer if above was helpful.
Thanks.
-TP