How can I make TeamViewer work from a 10.11.6 iMac to a 10.10.5 MacBook?

How can I remotely connect to and help a 10.10.5 MacBook (13-inch, Mid 2009) from my 10.11.6 iMac (Early 2009)?

I have tried TeamViewer 13.2 (on both Macs) without success. My version keeps saying:

«The remote TeamViewer is running an old version which is out of date.Therefore you can not connect to this Version anymore. Your connection partner can update TeamViewer by clicking on "Help" - "Check for new version".»

But my remote partner can not update to any newer version than 13.2 because 10.10.5 does not allow it - and the old Macbook can not be updatet beyond 10.10.5.

Anyone...?