To start the process, navigate to your Magento v2.x: Stores > Settings > Configuration > M2E Pro > Advanced Settings > Migration from Magento v1.x and click Proceed. You will be redirected to Step 1 of the Migration Wizard.
In Magento v1.x, go to System > Configuration > M2E Pro > Migration to Magento v2.x and click Proceed. It can take up to 15 minutes to stop the dynamic Cron tasks, put M2E Pro under maintenance, and prepare its database for migration. Wait until the process is completed, then get back to your Magento v2.x installation.
Before clicking Proceed, it is recommended to create a backup of M2E Pro data in case you need to restore it in Magento v1.x. Once you confirm the migration running, the process cannot be stopped.
In Magento v2.x, click Continue at Wizard Step 1. It will stop the dynamic Cron tasks, put M2E Pro under maintenance, and clear its database before the migration. Once the process is completed, you will be redirected to the next step.