Hi,
Normally you can re-schedule from your Certification dashboard. Similar to below screenshot:
If for some reason you are unable to reschedule via your dashboard you may contact Pearson VUE customer support:
https://home.pearsonvue.com/microsoft/contact
Additionally, 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 any questions/issues relating to exams/certification:
https://trainingsupport.microsoft.com/en-us/newthread?threadtype=Questions&forum=mcp
Please click Accept Answer if above was helpful.
Thanks.
-TP