How to connect my new domain to my old web hosting? Keeping my former domain to externa

Hello
I had website in OVH
With domain Fla . FR linked to web hosting Fla . fr (“fla” for the example)

We moved our hosting to another provider.
I changed the DNS for domain FlaFR to 55.xxxx (external host) and it worked

I took a new domain FLA . ovh to point to pour old website, because we still wanted to access the old pages.
The old website that is still hosted on Ovh server, on the FLA . FR hosting on the 213.xxxx

It seemed to work.
But when we go to Fla . ovh, it is slow and then redirects to Fla . fr and redirect to new website. (on external other hosting)

I looked on the Multi-site settings. I can still see the domain name fla . fr pointing to /www

How to remove the link from domain fla . fr and the hosting fla . fr ?

Thanks for your help
Thierry