To reseed the database via GUI:
1) Connect Remote Desktop to Passive Node
2) Open EMC
3) Go to Server Configuration-Mailbox
4) Select the Exchange server
5) Select the Storage Group
6) Right click the Storage Group you need to reseed, then select “Suspend Storage Group copy” , if it is not is suspended mode yet.
7) Right click the Storage Group you need to reseed, then select “Update Storage Group copy”
8) Select the Delete any existing log files in the target path check box
9) Then Next.
10) Click Update to seed the passive node with the database copy:
During the update process, you will be prompted to delete any obsolete checkpoint files that are found in the passive copy of the storage group, and any existing database file that is found in the passive copy of the storage group.After seeding has completed, click Finish to exit the wizard.
more info : http://technet.microsoft.com/en-us/library/bb124706(EXCHG.80).aspx