If i remember correctly, you must:
1. Quiesce transfers and break snapmirror relatonships from destination side, after that your destination volume will be rw.
2. You must reconnect your clients to destination svm to serve data.
3. After recovering source vol, you can reverse resync data from destination volume to source.
4. Break relationships again, but now from your source after syncronization and reconnect clients to source svm with restored vol.
5. Create resync again from source volume to destination volume.
All operations you can perform from web client.
Sorry, if there something wrong. I haven't practice with snapmirror 😞