Run PowerShell on MAM server (or the machine you are running the Migration Tool from) as Administrator.
Run following command:Uninstall-Module ExchangeOnlineManagement
Check there are no left-overs for EOM using command:Get-Module
Repeat he same by running 32-bit version of PowerShell (run as Admin)
Run the following command again:Uninstall-Module ExchangeOnlineManagement
Close the PowerShell (reboot the machine you are running the tool from) and run O365 Migration tool as Admin and connect again.
Tool will now install the required version of ExchangeOnlineManagement on background.
This may take several seconds