Hi,
You may contact Pearson VUE custom support to reschedule:
https://home.pearsonvue.com/microsoft/contact
To merge your accounts please ask your question in the Microsoft Credentials forum using link below. There are support moderators over there that will respond to your question in 1 business day and can assist:
https://trainingsupport.microsoft.com/en-us/newthread?threadtype=Questions&forum=mcp
Please click Accept Answer and upvote if above was helpful.
Thanks.
-TP