How 'groupify' a Restored SharePoint site that still has link to old deleted group?

[Denis Tiri]

A user deleted an Office 365 group.

We only noticed this after 30 days so restoring the group is not possible.
However the SharePoint site was still in the recyclebin.

I've been able to restore the SharePoint site.
But how can I now recreate the Office 365 group and link it to the existing SharePoint Site?

I do not get the "groupify" option on the restored SharePoint site (it still thinks it's connected to a deleted Group)

[#2]

Try to do it with PowerShell

[#3]

@Juan Carlos González Martín 

I'm trying with Set-SPOSiteOffice365Group, seems to work.

Still need to do some adjustments here and there, but looks fine.