Thank you! That helped! :)

As described in this post I have added a v1 to a v2 updated M5 network. Thev1 has a firmware of 2017 and does not get updated via the app menu.

https://community.tp-link.com/en/home/forum/topic/165402?replyId=341012

Now I have tried the instruction of making the v1 the main deco to get an update but when I follow the instruction mentioned in the link below I can set all the v2's as main deco but the v1 does noy show a an option to make a main deco.

https://www.tp-link.com/nl/support/faq/2400/

Please advise...kind regards

I had to make new network only for this single Deco. 

Thanks very much. You have pointed me to the right direction.

1. I created a new network onnly with the v1 m5 with firmware from 2017.

Create network

https://www.tp-link.com/us/support/faq/2295/

2. Connected the deco directly with ethenet to the Internet Modem.

3. Connected the wifi of my phone to the new network and

4. Than I could update the firmware

5. Go back to old network with other Deco's

6. Reset the v1 Deco and added the device to the old network

This al worked.