Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi Surya,
it is not feasible to extend an Office 365 for Business trial plan including the Dynamic CRM plan to 90 days. Only if a trial plan is within 15 days of expiring and the trial hasn’t been extended before then you can extend your trial for another 30 day period. Here is an article for your reference.
And for accessing CRM interface, you can refer to the following article:
https://msdn.microsoft.com/en-us/library/jj863696%28v=crm.6%29.aspx?f=255&MSPPError=-2147217396
Regards,
Yang