Xrmtoolbox provides a plugin “Auto Number Manager” that can be used to configure autonumbering for any entity in the CRM solution. Refer here for list of available plugin’s. Once AutoManager plugin is installed it will be available in the start up page of Xrmtool box

Once connected to CRM organization (aka Instance) the list of solutions will be displayed as per below and selecting a solution will display the list of entities for that solution:

In the following example autonumber format is set for the Account Number field of Member entity

The Number Format set in above is as per below

{PreFix}-{6 digit sequence number}-{Random String}

Seed value indicates the starting number of sequence

Click on Update once the format is acceptable.